A suction button unit for changeover between a suction source (14) and a suction opening (31) includes a piston chamber (53b) extending axially. A suction port hole (56) is formed at a lower end (53d) of the piston chamber, for connection with the suction opening. An exhaust port hole (57) is formed in a chamber inner wall (53e) of the piston chamber, for connection with the suction source. A piston rod (61, 100) is received in the piston chamber, has a first piston end (61a) protruding upwards, for shifting from a first position to a second position upon depression. The exhaust port hole is externally opened in case the piston rod is in the first position, but caused to communicate with the suction port hole in case the piston rod is in the second position. A tilting device (86, 102) tilts the piston rod relative to an axial direction of the piston chamber while the piston rod is in the first position.
