An image diagnostic apparatus includes a probe capable of light transmission and reception, wherein a reflection light in a coelom is obtained from the probe by scanning the probe rotatingly in the coelom, and a tomographic image in the coelom is formed and outputted based on the obtained reflection light. A light-shield is provided to shield the light transmitted to the probe, a connection detector detects whether or not the probe is connected, and a controller controls the light-shield based on a detected result by the connection detector.
