A switching valve unit for an endoscope apparatus, for changeover in a conduit extending between a suction source and a suction opening, comprising: a valve cylinder, mounted on a control handle of said endoscope apparatus, having a piston chamber; a cylinder opening formed at an upper end of said piston chamber; a suction port hole, formed at a lower end of said piston chamber, and adapted to connection with said suction opening; an exhaust port hole, formed in a chamber inner wall of said piston chamber, and adapted to connection with said suction source; a piston rod (61, 100), received in said piston chamber, having a first piston end protruding from said cylinder opening, for shifting from a first position to a second position upon depression; a side opening, formed in a peripheral side wall of said piston rod, closed by said chamber inner wall of said piston chamber in case said piston rod is in said first position, and aligned with said exhaust port hole in case said piston rod (61, 100) is in said second position; an end opening, formed at a second piston end of said piston rod (61, 100), for alignment with said suction port hole; a first flow path, formed in said piston rod between said side opening and said end opening, for communication of said exhaust port hole to said suction port hole in case said piston rod is in said second position; a peripheral groove, formed in said peripheral side wall of said piston rod (61, 100), aligned with said exhaust port hole in case said piston rod is in said first position, and closed by said chamber inner wall of said piston chamber in case said piston rod is in said second position; a flow path surface formed with said peripheral side wall of said piston rod to extend from said peripheral groove to said first piston end of said piston rod; a second flow path (73, 87-89), constituted by said peripheral groove and said flow path surface, for externally opening said exhaust port hole in case said piston rod is in said first position; and an anti-rotation device (55, 65) for preventing said piston rod from rotating relative to said piston chamber; characterized by a tilting device (86, 102) for tilting said piston rod relative to an axial direction of said valve cylinder while said piston rod is in said first position, wherein said tilting device (86, 102) is adapted to tilt said piston rod in a direction toward said side opening relative to said valve cylinder, for tightening closing of said side opening with said chamber inner wall. a valve cylinder, mounted on a control handle of said endoscope apparatus, having a piston chamber; a cylinder opening formed at an upper end of said piston chamber; a suction port hole, formed at a lower end of said piston chamber, and adapted to connection with said suction opening; an exhaust port hole, formed in a chamber inner wall of said piston chamber, and adapted to connection with said suction source; a piston rod (61, 100), received in said piston chamber, having a first piston end protruding from said cylinder opening, for shifting from a first position to a second position upon depression; a side opening, formed in a peripheral side wall of said piston rod, closed by said chamber inner wall of said piston chamber in case said piston rod is in said first position, and aligned with said exhaust port hole in case said piston rod (61, 100) is in said second position; an end opening, formed at a second piston end of said piston rod (61, 100), for alignment with said suction port hole; a first flow path, formed in said piston rod between said side opening and said end opening, for communication of said exhaust port hole to said suction port hole in case said piston rod is in said second position; a peripheral groove, formed in said peripheral side wall of said piston rod (61, 100), aligned with said exhaust port hole in case said piston rod is in said first position, and closed by said chamber inner wall of said piston chamber in case said piston rod is in said second position; a flow path surface formed with said peripheral side wall of said piston rod to extend from said peripheral groove to said first piston end of said piston rod; a second flow path (73, 87-89), constituted by said peripheral groove and said flow path surface, for externally opening said exhaust port hole in case said piston rod is in said first position; and an anti-rotation device (55, 65) for preventing said piston rod from rotating relative to said piston chamber; characterized by a tilting device (86, 102) for tilting said piston rod relative to an axial direction of said valve cylinder while said piston rod is in said first position, wherein said tilting device (86, 102) is adapted to tilt said piston rod in a direction toward said side opening relative to said valve cylinder, for tightening closing of said side opening with said chamber inner wall.