In transmitting images picked up by an intrabody introduced device to outside a test body, synchronizing signals of the image signal are set to signal patterns in the same high-frequency band as for the image signal and not used for the image signal. This enables a receiver to stably binarize the synchronizing signal and thus to acquire favorable image signal. For example, in a clipping circuit provided in a signal processing circuit in a capsule type endoscope (an example of an intrabody introduced device), image information of a high-intensity portion is clipped out of image information acquired by an imaging section and a pattern generation circuit allocates signal patterns within the clipped intensity range as horizontal and vertical synchronizing signals.