A flow channel switching valve (1, 2, 3, 4) comprising: a main valve housing forming a main valve chamber; a first main valve mount arranged within the main valve chamber, the first main valve mount having a valve seat face with a plurality of ports (pA, pB, pF); a second main valve mount arranged within the main valve chamber opposite to the first main valve mount with respect to an axis of the main valve chamber, the second main valve mount having a valve seat face with a plurality of ports (pC, pD, pE); and a main valve element arranged within the main valve chamber in a movable manner in the axial direction, the main valve element including a pair of slide valve elements (15A, 15B) of a high-pressure side slide valve element and a low-pressure side slide valve element, the high-pressure side slide valve element being slidable on the valve seat face of the first main valve mount and having a high-pressure side U-turn passage adapted to receive a relatively high-pressure fluid, the low-pressure side slide valve element being slidable on the valve seat face of the second main valve mount and having a low-pressure side U-turn passage adapted to receive a relatively low-pressure fluid, wherein: the pair of slide valve elements (15A, 15B) is integrally movable in the axial direction and individually slidable in a direction perpendicular to the axis, the main valve element is moved within the main valve chamber so that communication of the plurality of ports (pA, pB, pC, pD, pE, pF) in each of the first main valve mount and the second main valve mount is switched, characterized in that the pair of slide valve elements (15A, 15B) includes an annular seal face around an opening of the high-pressure side U-turn passage of the high-pressure side slide valve element, the annular seal face being adapted to be in contact with the valve seat face, and an annular seal member is disposed between the high-pressure side slide valve element and the low-pressure side slide valve element, wherein, as seen in the direction perpendicular to the axis, an outer shape of a pressure receiving face of the high-pressure side slide valve element adjacent to the low-pressure side slide valve element, which is the outer shape of the seal member, is set larger than an outer shape of the annular seal face. a main valve housing forming a main valve chamber; a first main valve mount arranged within the main valve chamber, the first main valve mount having a valve seat face with a plurality of ports (pA, pB, pF); a second main valve mount arranged within the main valve chamber opposite to the first main valve mount with respect to an axis of the main valve chamber, the second main valve mount having a valve seat face with a plurality of ports (pC, pD, pE); and a main valve element arranged within the main valve chamber in a movable manner in the axial direction, the main valve element including a pair of slide valve elements (15A, 15B) of a high-pressure side slide valve element and a low-pressure side slide valve element, the high-pressure side slide valve element being slidable on the valve seat face of the first main valve mount and having a high-pressure side U-turn passage adapted to receive a relatively high-pressure fluid, the low-pressure side slide valve element being slidable on the valve seat face of the second main valve mount and having a low-pressure side U-turn passage adapted to receive a relatively low-pressure fluid, wherein: the pair of slide valve elements (15A, 15B) is integrally movable in the axial direction and individually slidable in a direction perpendicular to the axis, the main valve element is moved within the main valve chamber so that communication of the plurality of ports (pA, pB, pC, pD, pE, pF) in each of the first main valve mount and the second main valve mount is switched, characterized in that the pair of slide valve elements (15A, 15B) includes an annular seal face around an opening of the high-pressure side U-turn passage of the high-pressure side slide valve element, the annular seal face being adapted to be in contact with the valve seat face, and an annular seal member is disposed between the high-pressure side slide valve element and the low-pressure side slide valve element, wherein, as seen in the direction perpendicular to the axis, an outer shape of a pressure receiving face of the high-pressure side slide valve element adjacent to the low-pressure side slide valve element, which is the outer shape of the seal member, is set larger than an outer shape of the annular seal face. the pair of slide valve elements (15A, 15B) is integrally movable in the axial direction and individually slidable in a direction perpendicular to the axis, the main valve element is moved within the main valve chamber so that communication of the plurality of ports (pA, pB, pC, pD, pE, pF) in each of the first main valve mount and the second main valve mount is switched, characterized in that the pair of slide valve elements (15A, 15B) includes an annular seal face around an opening of the high-pressure side U-turn passage of the high-pressure side slide valve element, the annular seal face being adapted to be in contact with the valve seat face, and an annular seal member is disposed between the high-pressure side slide valve element and the low-pressure side slide valve element, wherein, as seen in the direction perpendicular to the axis, an outer shape of a pressure receiving face of the high-pressure side slide valve element adjacent to the low-pressure side slide valve element, which is the outer shape of the seal member, is set larger than an outer shape of the annular seal face.