A channel switch valve, comprising: a valve shaft, a driving source to rotary drive the valve shaft, and a valve body including an inflow port, a plurality of outflow ports (21, 22), a valve shaft insertion space, into which the valve shaft is fitted and inserted rotatably, and a valve seat (15A, 15B) disposed at lower periphery of the valve shaft insertion space, wherein outflow openings (23, 24) each serving as a starting end of the corresponding one of the outflow ports are disposed at the valve seat, a thick and disk-shaped or a short cylindrical valve element is disposed integrally with the valve shaft at a lower end of the valve shaft so as to protrude below from the valve seat, and the valve shaft with the valve element is slidable in the valve shaft insertion space in an axial direction of the valve shaft within a predetermined range, a space for valve element is disposed below the valve seat so as to house the valve element therein, the inflow port being disposed below the space for valve element, the valve element has at least one passage opening (41, 42) to let the inflow port and each outflow port open in a selectable manner, the valve shaft with the valve element is rotatable, whereby the valve at least has a first circulating state, in which fluid flows from the inflow port to one of the outflow ports via the passage opening, and a second circulating state, in which fluid flows from the inflow port to another outflow port via the passage opening in a selectable manner, characterized in that the valve shaft with the valve element is arranged such that, when pressure at any one of the outflow ports increases to predetermined pressure or more, the valve shaft with the valve element is pushed downward so as to create a gap between the valve seat and an upper face of the valve element, whereby pressurized fluid on the outflow port side is allowed to flow to the inflow port side. outflow openings (23, 24) each serving as a starting end of the corresponding one of the outflow ports are disposed at the valve seat, a thick and disk-shaped or a short cylindrical valve element is disposed integrally with the valve shaft at a lower end of the valve shaft so as to protrude below from the valve seat, and the valve shaft with the valve element is slidable in the valve shaft insertion space in an axial direction of the valve shaft within a predetermined range, a space for valve element is disposed below the valve seat so as to house the valve element therein, the inflow port being disposed below the space for valve element, the valve element has at least one passage opening (41, 42) to let the inflow port and each outflow port open in a selectable manner, the valve shaft with the valve element is rotatable, whereby the valve at least has a first circulating state, in which fluid flows from the inflow port to one of the outflow ports via the passage opening, and a second circulating state, in which fluid flows from the inflow port to another outflow port via the passage opening in a selectable manner, characterized in that the valve shaft with the valve element is arranged such that, when pressure at any one of the outflow ports increases to predetermined pressure or more, the valve shaft with the valve element is pushed downward so as to create a gap between the valve seat and an upper face of the valve element, whereby pressurized fluid on the outflow port side is allowed to flow to the inflow port side.