A flow channel switching valve (1, 2) comprising: a valve body including a valve chamber, an upper inlet/outlet port, an intermediate inlet/outlet port, and a lower inlet/outlet port opening in the valve chamber, an upper valve orifice provided between the upper inlet/outlet port and the intermediate inlet/outlet port, and a lower valve orifice provided between the intermediate inlet/outlet port and the lower inlet/outlet port; a valve element disposed in the valve chamber in a vertically movable manner and including an upper valve element portion and a lower valve element portion separated from each other in a vertical movement direction, the upper valve element portion and the lower valve element portion being adapted to control a flow rate of a fluid flowing through the upper valve orifice and the lower valve orifice; and a vertical movement drive unit provided on an upper side of the valve element so as to move up or down the valve element, wherein the lower valve element portion is formed to have a smaller diameter than that of the upper valve orifice and the lower valve orifice, and can be inserted into an inside of the lower valve orifice through the upper valve orifice, and a bottom portion of the valve body is a lower stopper adapted to define a lowest position of the valve element, characterized in that the vertical movement drive unit includes a stepping motor including a stator and a rotor, wherein a valve stem holder and the rotor are coupled together by a support ring, a thread feeding mechanism including a fixed thread portion formed on the outer periphery of a guide bush that is securely fitted by press-fitting at the lower end thereof to the fitting hole provided in the center of the upper part of the valve body and a movable thread portion formed on the inner periphery of the valve stem holder and screwed into the fixed thread portion, and a stopper mechanism for limiting the rotation and downward movement of the valve stem holder, said stopper mechanism including a lower stopper element securely attached to the outer periphery of the guide bush and an upper stopper element securely attached to the outer periphery of the valve stem holder. a valve body including a valve chamber, an upper inlet/outlet port, an intermediate inlet/outlet port, and a lower inlet/outlet port opening in the valve chamber, an upper valve orifice provided between the upper inlet/outlet port and the intermediate inlet/outlet port, and a lower valve orifice provided between the intermediate inlet/outlet port and the lower inlet/outlet port; a valve element disposed in the valve chamber in a vertically movable manner and including an upper valve element portion and a lower valve element portion separated from each other in a vertical movement direction, the upper valve element portion and the lower valve element portion being adapted to control a flow rate of a fluid flowing through the upper valve orifice and the lower valve orifice; and a vertical movement drive unit provided on an upper side of the valve element so as to move up or down the valve element, wherein the lower valve element portion is formed to have a smaller diameter than that of the upper valve orifice and the lower valve orifice, and can be inserted into an inside of the lower valve orifice through the upper valve orifice, and a bottom portion of the valve body is a lower stopper adapted to define a lowest position of the valve element, characterized in that the vertical movement drive unit includes a stepping motor including a stator and a rotor, wherein a valve stem holder and the rotor are coupled together by a support ring, a thread feeding mechanism including a fixed thread portion formed on the outer periphery of a guide bush that is securely fitted by press-fitting at the lower end thereof to the fitting hole provided in the center of the upper part of the valve body and a movable thread portion formed on the inner periphery of the valve stem holder and screwed into the fixed thread portion, and a stopper mechanism for limiting the rotation and downward movement of the valve stem holder, said stopper mechanism including a lower stopper element securely attached to the outer periphery of the guide bush and an upper stopper element securely attached to the outer periphery of the valve stem holder. a stepping motor including a stator and a rotor, wherein a valve stem holder and the rotor are coupled together by a support ring, a thread feeding mechanism including a fixed thread portion formed on the outer periphery of a guide bush that is securely fitted by press-fitting at the lower end thereof to the fitting hole provided in the center of the upper part of the valve body and a movable thread portion formed on the inner periphery of the valve stem holder and screwed into the fixed thread portion, and a stopper mechanism for limiting the rotation and downward movement of the valve stem holder, said stopper mechanism including a lower stopper element securely attached to the outer periphery of the guide bush and an upper stopper element securely attached to the outer periphery of the valve stem holder.