1. An apparatus for detecting an object for a vehicle, the apparatus comprising: a camera unit configured to output a surrounding image of a vehicle; and a circuitry configured to: set a reference square having a minimum height and a minimum width on the surrounding image, calculate center coordinates of a lower end of the reference square in each region of the surrounding image and a height threshold value which is variable according to the center coordinates of the lower end of the reference square, while moving the reference square on all regions of the surrounding image, store height threshold values each corresponding to each center coordinates of the lower end of the reference square in a look-up table, set an object square surrounding an object candidate on the surrounding image of the vehicle, calculate center coordinates of a lower end of the object square, output a filtered image by extracting the height threshold value corresponding to center coordinates of the lower end of the object square from the look-up table and excluding an object having a height equal to or smaller than the height threshold value corresponding to the center coordinates of the lower end of the object square from the object candidate on the surrounding image of the vehicle, and detect a specific object from the output filtered image.