1. An apparatus for generating a thermal image regarding a target object, the apparatus comprising: a memory configured to store a first thermal image; a first sensor configured to measure a temperature of the target object; a second sensor configured to measure a distance to the target object; a third sensor configured to detect a movement of the thermal image generating apparatus; a controller configured to: generate a second thermal image based on temperature information received from the first sensor, distance information received from the second sensor, and movement information received from the third sensor, and generate a third thermal image based on the first thermal image and the second thermal image; and a display configured to display the third thermal image, wherein the distance information includes measured distances between the thermal image generating apparatus and the target object, and wherein the controller is further configured to: compare the distance information related to the second thermal image and distance information related to a portion of the first thermal image overlapping with the second thermal image, when, a measured distance between the thermal image generating apparatus and the target object at which the second thermal image is generated is shorter than a measured distance between the thermal image generating apparatus and the target object at which the first thermal image is generated, generate the third thermal image by replacing the portion of the first thermal image with the second thermal image, and when the measured distance at which the second thermal image is generated is longer than or equal to the measured distance at which the first thermal image is generated, not replace the portion of the first thermal image with the second thermal image.