An ultrasonic surgical apparatus for crushing, sucking and removing undesirable substances inside the body such as an ulcerous tissue, thrombus and calcium clod by means of mechanical vibrations of a flexible ultrasonic probe (17). The surgical apparatus comprises a horn (5) connected to an ultrasonic vibration source (4) and adapted to transmit and amplify mechanical vibrations of an ultrasonic frequency, an ultrasonic probe (17) including a flexible linear transmitting member (44) having a working portion (21) adapted to effect mechanical vibration of an ultrasonic frequency, a horn cover (6) at least a portion of which is made of a flexible material, and a flexible tube (8) having three inner holes and three branch tubes communicating with the inner holes and connected to the horn cover (6) through the one branch tube (7). The ultrasonic probe (17) is disposed in one of the inner holes (20) communicated with the latter one branch tube (7), and a suction device (11) and a liquid injector (14) are connected to two of the branch tubes.