driven gear 64 mounted around an upper portion of the body 62 so as to be engaged with the driving gear 56 of the actuator 26 such that the filler cap is actuated if the motor 52 of the actuator 26 generates a rotational force the second sensor 30 is provided with two second sensor terminals 70 mounted inside the fuel inlet and electrically connected to the battery 42 and second relay 68 respectively such that an electric connection is established when is the second conductor 66 is located between the two second sensor terminals 70 when the filler cap 28 is placed in the fuel inlet the operation of the filler cap assembly according to the present invention will be described hereinafter fig2 shows the filler cap assembly as closed in this state if the opening lever 34 is pulled a locking device 76 that is pivotally connected to an end of the cable 58 and hooked on a hook 78 formed on an inner surface of the fuel tank door 32 is released such that the fuel tank door 32 is opened by an elastic force of a torsion spring arranged with a hinge mechanism which pivotally connects the fuel tank door 32 to the vehicle body at the same time the first conductor 38 which is fixed on the cable 58 moves in the opening lever direction against the coil spring 48 and connects the two first sensor terminals such that electrical continuity is established between the battery 42 and the motor 52 of the actuator via the first relay 44 and the first transistor 50 electric current from the battery 42 is amplified by.