A flow channel switching valve comprising: a valve body that has a valve chamber and flow channels in communication with the valve chamber ; a valve member that is installed in the valve chamber and that has a switching flow channel therein for switching between connections of the flow channels depending on a rotational position of the valve member ; a pair of seat members that is installed in the valve chamber in an interval, that interposes the valve member therebetween, and that rotatably supports the valve member ; a sealing member that is disposed between each seat member and the valve body ; and a rotation driving section that causes the valve member to rotate about a rotation axis, wherein the valve body is integrally provided with the flow channels , wherein the valve body has an opening that is in communication with the valve chamber and that is used for inserting the valve member , the pair of seat members , and the sealing member during assembly, wherein a size of the valve member in a direction of the rotation axis is smaller than a size thereof in a direction perpendicular to the rotation axis, and wherein a first jig mounting portion for rotating the valve member in the perpendicular direction is disposed on an inner wall surface of the valve member that is visible from a location outside the valve body through the opening or the flow channels , wherein the valve member has three valve member openings that face in the direction perpendicular to the rotation axis and that are connected to each other by using the switching flow channel , wherein the three valve member openings are arranged about the rotation axis in an interval of 90 degrees, wherein diameters of two valve member openings opposite each other with the rotation axis interposed therebetween among the three valve member openings are smaller than a diameter of the other valve member opening , wherein the inner wall surface of the valve member on which the first jig mounting portion is disposed is opposite the other valve member opening . wherein the valve body is integrally provided with the flow channels , wherein the valve body has an opening that is in communication with the valve chamber and that is used for inserting the valve member , the pair of seat members , and the sealing member during assembly, wherein a size of the valve member in a direction of the rotation axis is smaller than a size thereof in a direction perpendicular to the rotation axis, and wherein a first jig mounting portion for rotating the valve member in the perpendicular direction is disposed on an inner wall surface of the valve member that is visible from a location outside the valve body through the opening or the flow channels , wherein the valve member has three valve member openings that face in the direction perpendicular to the rotation axis and that are connected to each other by using the switching flow channel , wherein the three valve member openings are arranged about the rotation axis in an interval of 90 degrees, wherein diameters of two valve member openings opposite each other with the rotation axis interposed therebetween among the three valve member openings are smaller than a diameter of the other valve member opening , wherein the inner wall surface of the valve member on which the first jig mounting portion is disposed is opposite the other valve member opening . <EOS>