larger than given opening a it assumes a downstream position relative to port 34 but an upstream position relative to the port 107 accordingly a vacuum above given vacuum level v2 is supplied to vacuum operating chamber 113 in vacuum switch 111 so that contact element 115 is separated from terminals 116 and 117 solenoid 105 in electromagnetic valve 101 is there de energized and plunger 104 is separated from port 103 under the action of the coil spring 106 thus gasoline vapor is supplied to engine 6 through ports 102 and 103 and then through purge port 17 fig1 is the tenth embodiment of the fuel evaporation control system according to the present invention this embodiment is a modification of the embodiment of fig1 in this embodiment as well like parts are designated by like reference numerals in common with those given in fig1 in the embodiment of fig1 a computer 123 is used for operating solenoids 36 and 105 in electromagnetic valves 35 and 101 in place of a vacuum switch the terminals of solenoids 36 and 105 in electromagnetic valves 35 and 101 are connected to the output terminals 123a and 123b of the computer 123 respectively output terminals 123c and 123d of computer 123 are connected to the interrupter of ignition distributer 124 and to throttle switch 125 respectively when the throttle valve is at an idling opening and the rotational speed of the engine is higher than the idling speed i e during engine deceleration input terminal 123a of the computer 123 is grounded while the input terminal 123b is disconnected.