dotted dashed line in the figure and closes the intake gas pipe 9 that communicates with the jet pump 8 when the control valve body 31 is moved upwards by suction of a plunger 32 a the intake gas valve 9 is opened the stopcock 11 a is moved upwards and the vent valve 11 is closed off if the liquid surface rises when the solenoid 32 is not excited the vent valve 11 will be closed off by the rise of the float 11 b however because the connecting part 11 d can be moved irrespective of the control valve body 31 the intake gas valve 9 stays closed the solenoid 32 the a valve 18 the b valve 19 the bypass valve 24 the internal pressure sensor 14 and the fuel level gauge 22 are connected to the cpu of the fuel injection control device and the cpu performs open close control of each valve and sensing through the internal pressure sensor 14 and the fuel level gauge 22 with the control valve 10 of embodiment 2 being rendered the control valve body 31 which is open close controlled contrariwise to the vent valve 11 of the vent valve device 30 the leak judgment of embodiment 3 has the same judgment procedure as embodiment 2 and consequently explanation thereof is omitted here in embodiment 3 since the vent valve 11 and the control valve 10 are configured as one unit in the vent valve device 30 the apparatus for detecting gas leaks and control can be simplified fig8 is a.