PURPOSE: To eliminate that the insertion of treatment instruments becomes impossible because of mutual collision or the positional relation between them is not constant, by providing one treatment instrument so as to shift the center axis of the mouth thereof from that of the mouth of the other treatment instrument.

CONSTITUTION: When an ultrasonic probe 15 is inserted from the first tube body 9 and a basket catheter 16 is subsequently inserted from the second tube body 11, the axial line (a) of the first tube body 9 of a connection mouth body 8 and the axial line (b) of the second tube body 11 are shifted by a dimension (d) in the lateral direction crossing the vertical line (c) of the connection mouth body 8 at a right angle and the basket catheter 16 is positioned on the left side of the ultrasonic probe 15 when looked on the leading end side of an insert part 2. Moreover, because of the presence of the shift dimension (d), it is prevented that the insertion of the basket catheter 16 becomes impossible by the collision with the ultrasonic probe 15. Therefore, the ultrasonic probe 15 can be smoothly inserted into a treatment instrument pipe 22.