The invention discloses a technique, by which a suitable radius of curvature can be obtained so that small type ultrasonic probe will be closely fitted to human body and by which an ultrasonic probe adaptable for human superficial tissues can be provided. According to this technique, the invention provides a frame 5 to constitute a part of a cubicle, a motor 1 fixed on said frame, a first arm 6 with one end fixed on a rotating shaft 7 of said motor, and a second arm 8 with one end rotatably coupled with the other end of said first arm via a coupling shaft 9 and with the other end having an ultrasonic element mounted thereon, said second arm has a lengthwise long groove 11 and is slidably engaged with the fixed shaft of said frame in the direction of length, a length from an end of said second arm where said ultrasonic element is mounted on said coupling shaft is designed to be longer than the length from said rotating shaft to said coupling shaft, and further, to be longer than the length from said rotating shaft to said fixed shaft, and a swinging mechanism comprising said first arm and said second arm is disposed in said cubicle surrounded by an ultrasonic window and by said frame and is sealed with an acoustic coupling liquid.
