To prevent the occurrence of unusual wear on a seat surface by reducing contact pressure on the valve box side seat surface of the valve element of a three-way valve with two outflow ports for one inflow port.

This two-port slide valve in which one slide valve 1 is reciprocatingly slid between two parallel outflow ports 2, 2 to change the direction of outflow includes a supporting guide 4, flat with the surface of a valve seat 3, provided between the valve seats 3 of the slide valve 1 for the outflow ports 2 and a sliding face 7, in contact with the supporting guide 4, provided on the side face of the valve seat of the slide valve 1.