To detect a small-sized and low-luminance target by correcting the amount of inter-frame slippage of picture images caused by a difference in imaging conditions.

In the event that the target is imaged while a flying body AP is in flight, firstly, a flying speed/altitude detector 16 detects the altitude and flying speed of the own flying body AP to be detected. In addition to this detection result, imaging conditions such as the visual axis direction of an imaging device 11 obtained from a gimbal mechanism part 12, an imaged visual field obtained from the imaging device 11, and imaging intervals, are acquired. From these acquired imaging conditions, an image flow size computing part 15 finds the size of a flow arising dependently on a distance within a visual field of the imaging device for each of frame picture images. An image flow size correcting part 15 shifts the size of flow of a picture image in a video signal dependently on the found size of flow for each frame. Correlation between frames is found by a frame integration processing part 18, thereby detecting the target within the scanning range of the imaging device 11.