Abstract: Electric power is supplied to a coil (17) to drive a valve (16) for displacement by a magnetic action, thereby adjusting the opening of a valve path (43). The electric power for thus driving the valve (16) is supplied to the coil (17) through an electric conductor wire (18). The electric conductor wire (18) extends from a portion of a housing (15) that is exposed from a tank (11) to a portion of the housing (15) that accommodates the coil (17) therein. Thus, the housing (15) holds the electric conductor wire (18) as extending inside the housing (15). Since the electric conductor wire (18) is thus held as extending inside the housing (15), the electric conductor wire (18) is protected against vibration and impact given thereto from the outside. Thus, the electric conductor wire (18) has enhanced reliability in terms of resistance to vibration and impact. With the electric conductor wire (18) thus positioned within the housing (15), the housing (15) can house the electric conductor wire (18) neatly.