A pressure reducing valve device includes a first body; a second body; a valve mechanism accommodated in the first body, and including a valve seat and a valve element; and a piston that is accommodated in the second body, defines a pressure reducing chamber, and is configured to move in accordance with a pressure in the pressure reducing chamber so as to move the valve element. The first body is connected to an inner portion of a connection portion having a bottomed cylindrical shape. The connection portion is provided in the second body to protrude outward. The valve seat is held between the first body and the second body in a direction in which the first body and the second body are attached to each other such that the valve seat is fixed in a flow passage.