An ultrasonic diagnostic apparatus includes one transmitting coil arranged in the longitudinal direction of an endoscope inserting portion in an ultrasonic endoscope, and another transmitting coil for detecting the position and the direction, which detects the position and the direction of a tomographic plane when forming a tomogram at a distal end portion of an inserting portion by an ultrasonic vibrator. A coil energizing signal is applied to both the transmitting coils so as to generate magnetic field. The magnetic field is detected by receiving coils. A position and direction calculating circuit detects positional data of the one transmitting coil and positional and directional data of the other transmitting coil. The calculated data is transmitted to an auxiliary-image forming circuit which forms an image of an inserting shape and an auxiliary image indicating the position and the direction of the tomographic plane. It is easily understood which image in the celom the observed tomogram is by displaying both the auxiliary image and the tomogram on a display device.
