To provide a flow passage changeover unit easily adjusting a route opening and closing means for controlling a circulation condition of gas, and a suction retention unit and a pressure operation unit using the flow passage changeover unit.

This invented flow passage changeover unit is provided with a main body 11 constructed to enable gas circulation and provided with a ventilation route 11S provided with an intermediate opening part 11P in a middle of the route, and a route opening and closing means 13 opening and closing at least a part of the ventilation route in a downstream of the intermediate opening part in the ventilation route. The route opening and closing means faces an end part opening 11Sb of the ventilation route from an outside, and is provided with a operation part 13b constructed movably in a predetermined operation direction and materializing open and close operation of the ventilation route, and a drive mechanism 13c driving the operation part in an operation direction from a predetermined standard section 13a where the operation part is supported by a main body, and includes position adjustment means 12, 18, 11c constructed in such a manner that position can be adjusted in the operation direction in relation to a main body of the standard section.