The ultrasonic CT device includes: a first water tank configured such that an object is inserted therein, the first water tank being filled with a medium through which an ultrasonic wave passes; a ring array that irradiates an ultrasonic wave to the object and detects an ultrasonic wave reflected by the object while moving on an outer surface of the first water tank; and a signal processing unit that generates a tomographic image of the object based on a signal obtained by the ring array. The ultrasonic CT device further includes: a second water tank that houses the first water tank and the ring array; and a lid having a hole or a notch which is provided on a side of the object in the second water tank and which drains the medium.