The utility model provides a cover locking device which can reduce resistance in closing a cover. According to the cover locking device (10), a power transmission mechanism is arranged between a motor (40) and a locking component (50) and composed of a worm (47), a worm gear (43), a pressing protruding part (41), a pressed surface (54A) and an interference-avoidance space (54S). The power transmission mechanism transmits rear propulsion power enabling the locking component (50) to retreat to a locking release position to the locking component (50) from the motor (40), but power is resisted between the locking component (50) and the motor (40) instead of being transmitted from the locking component (50) to the motor (40), namely, when the cover (94) is closed, the rear propulsion power is received by the locking component (50) from a clamping protruding piece (95) of the cover (94) and then resisted by the power transmission mechanism instead of being transmitted to the motor (40).