A flow channel switching valve includes a valve stem that is attached to a ball valve member. The flow channel switching valve includes a potentiometer shaft that is press-fitted into an attachment hole provided in an end surface of the valve stem, and a potentiometer that detects a rotation angle of the potentiometer shaft around an axis. The potentiometer shaft has a small-diameter portion, a medium-diameter portion, and a large-diameter portion that are sequentially connected in a direction of the axis, and is supported rotatably around the axis in the attachment hole in an inserted state before being press-fitted into the attachment hole. The large-diameter portion is press-fitted into an upper end portion of the attachment hole.