exemplary embodiments of the present invention are described in more detail with reference to the accompanying drawings . in the following description , the same or corresponding components as in conventional systems will be provided with the same reference numerals . as illustrated in fig4 and 5 , a nondestructive testing apparatus for a blade root of a steam turbine installed in nuclear plants and thermal plants , performing the testing using a probe , includes an ultrasonic probe fixing unit 200 for testing a blade 110 of the steam turbine and an encoder fixing unit 300 for recording a rotation distance of a rotating turbine rotor 100 . referring to fig4 and fig6 , the ultrasonic probe fixing unit 200 includes a magnetic body 201 switchably fixed to a fixture supporter 151 , a first steel shaft 202 fixed vertically to its own magnetic body 201 , a second steel shaft 204 connected to the first steel shaft 202 through a first joint 203 in a horizontal posture with respect to the figure and having a three - dimensional degree of freedom , that is , rotatable and vertically movable , and a contacting pressure controller 205 including a driving motor 206 , a motional direction converter 207 and a load cell 208 that are mounted to the second steel shaft 204 to control a contacting force applied to an ultrasonic probe 210 , and the ultrasonic probe 210 connected to a leading end of the second steel shaft 204 through a second joint 209 . the encoder fixing unit 300 , as illustrated in fig5 and fig7 , includes a magnetic body 301 switchably fixed to the fixture supporter 151 , a first steel shaft 302 vertically fixed to the magnetic body 301 , a second steel shaft 304 connected to the first steel shaft 302 through a first joint 303 in a horizontal posture with respect to the figure and having a three - dimensional degree of freedom , that is , rotatable and vertically movable , and an encoder 305 mounted to the second steel shaft 304 to be rotatable by 360 degrees so as to measure the rotation distance of the turbine rotor 100 . in the above - structured ultrasonic probe fixing unit 200 , the magnetic body 201 is switchably attached to the fixture supporter 151 and the first steel shaft 202 is fixed to the magnetic body 201 in a vertical posture . since the second steel shaft 204 is connected to the first steel shaft 202 in a horizontal posture through the first joint 203 , the second steel shaft 204 accordingly has a three - dimensional degree of freedom , that is , being movable vertically along the first steel shaft 202 through the first joint 203 and rotatable by 360 degrees . the second steel shaft 204 is equipped with the contacting pressure controller 205 for maintaining a predetermined pressure between the ultrasonic probe 210 and the blade 110 of the steam turbine , which is a tested object . the contacting pressure controller 205 reads a force value of the load cell 208 equal to the pressure transmitted from the ultrasonic probe 210 through the second joint 209 , and converts the rotational motion of the driving motor 206 to the linear motion at the motional direction converter 207 by comparing the read value with a preset value of the load cell 208 . as the second joint 209 is pushed and pulled by the linear motion , the contacting pressure of the ultrasonic probe 210 is controlled so that the ultrasonic probe 210 can contact to a desired position of the blade 110 of the steam turbine , which is the tested object . the ultrasonic probe fixing unit 200 is capable of bringing the ultrasonic probe 210 into contact with the blade 110 of the steam turbine without an additional operation in a state where a casing of the steam turbine is opened . when the ultrasonic probe 210 is in contact with the blade 110 , the steam turbine is rotated at a regular speed by an operation motor mounted to the steam turbine , thereby providing the testing to be performed omnidirectionally through 360 degrees . in order to perform the automatic testing , it is necessary to record the rotation distance of the turbine rotor 100 . for this purpose , the encoder 305 needs to be attached to a proper position on a body of the steam turbine , to be accessible to the rotating steam turbine at any position . as a device for attaching the encoder 305 , the encoder fixing unit 300 illustrated in fig7 may be appropriately applied . the encoder fixing unit 300 , while supporting the encoder 300 , brings the encoder 305 into contact with the rotating steam turbine by exerting a predetermined force in a desired direction . in the same manner as the ultrasonic probe fixing unit 200 , the encoder fixing unit 300 is also rotatable by 360 degrees by the first steel shaft 302 , the second steel shaft 304 , and the first joint 303 , and therefore is contactable to a desired position as illustrated in fig5 . after the fixture supporter 151 for the ultrasonic probe fixing unit 200 and the encoder fixing unit 300 is mounted , when the testing of one stage is completed , the second joint 204 is rotated by 180 degrees as indicated by an arrow in fig8 to perform testing with an adjoining stage . therefore , the root 130 of the blade 110 disposed at the opposite side can be tested . as explained above , the testing apparatus hereof is able to perform testing with the roots 130 of the blades 110 of the discs 120 on both sides at one position . consequently , the testing time and the manpower can be considerably saved . meanwhile , as illustrated in fig8 , an ultrasonic signal from the ultrasonic probe 210 and the rotation distance according to rotation of the turbine rotor 100 are detected by the encoder 305 , and received by a general ultrasonic transceiver 530 . the received signal is stored in a general personal computer ( pc ) 510 through a local area network ( lan ) to be analyzed and utilized as the result of the testing . fig9 is a graph displaying a state of the ultrasonic nondestructive testing performed on the pc 510 using the ultrasonic probe 210 . in order to perform the ultrasonic nondestructive testing , the ultrasonic probe 210 needs to contact with the tested object through a contacting medium so as to transmit ultrasonic waves to a surface of the tested object . therefore , a general contacting medium is supplied from an outlet of a contacting medium supplier 550 through a hose 560 . generally , in order to obtain signals with excellent sensitivity during the ultrasonic nondestructive testing , the ultrasonic probe 210 is required to contact with the surface of the tested object by a predetermined pressure . accordingly , the load cell 208 and the driving motor 206 are provided at a rear end of the ultrasonic probe 210 such that the ultrasonic probe 210 operates the regular pressure against the disc 120 . when a conventional testing apparatus is used , it takes about 5 to 12 hours for only installing the testing apparatus . however , the testing apparatus hereof demands just 20 to 30 minutes , thus highly saving the installing time . in addition , it takes less than even 10 hours for opening the steam turbine casing , withdrawing the steam turbine and transferring the steam turbine to the testing place as preparation for the testing . therefore , the time for preparing the testing can be remarkably reduced . moreover , when using the conventional testing apparatus , it can take more than an hour to move to the next stage after the testing with one stage . on the contrary , the testing apparatus hereof may require only about 5 minutes to do the same . to summarize , the testing apparatus according to example embodiments of the present invention is capable of performing a nondestructive testing stably in a simple manner . furthermore , the time for testing the steam turbine can be greatly reduced . as should be appreciated from the above description , example embodiments of the present invention may solve various problems occurring when the steam turbine is tested by the conventional testing apparatus . for example , since considerable time is required from withdrawing the steam turbine for the testing to completing the nondestructive testing , a testing term should sometimes be extended during the operation of the power plant . however , the nondestructive testing apparatus according to example embodiments of the present invention effectively saves time for being installed and removed . reliability of the testing result can be highly enhanced . in addition , it becomes easier to find and evaluate a defect of the testing apparatus . although example embodiments of the present invention have been described for illustrative purposes , those skilled in the art should appreciate that various modifications , additions and substitutions are possible , without departing from the scope and spirit of the present invention .