A battery cover opening/closing device which prevents a battery from being opened when the power switch is in the on position and prevents the switch from being turned on when the cover is not completely closed. The device includes a cover opening member (21), a power switch manipulator (51) for turning on and off the power switch for the battery and a safety mechanism for enabling the opening operation of the cover opening member (21) only when the power switch manipulator (51) is in the position of turning off the power switch. The safety mechanism comprises a slide-locking plate (14) having an opening/closing hole means (20) in which a bar coupled to the member integrally therewith is fitted. The opening/closing hole means includes an entry hindrance hole (20b) which does not allow the member (21) to be pressed to open the cover when the manipulator is in the position of turning on the power switch and an entry allowance hole (20a) which is continuous to the entrance hindrance hole (20b) and allows the member (21 ) to be pressed to open the cover when the manipulator is in the position of turning off the switch.