This locking device is provided with: a lever that is rotatably provided to a cover and that is switched from an initial state to an operating state in opposition to energizing force or gravity; a locking rod that slides in interlocking fashion in association with rotation of the lever; and braking means, the cover being locked to the main unit side through the agency of the locking rod, and being switched to the unlocked state through rotation of the lever, wherein the device is characterized in that the braking means is a rotary damper that has a geared braking shaft, that is installed, with respect to the lever, in approximate alignment to the rotation center of the lever, and that brakes the lever and the locking rod; and by having an acting gear arranged in a state of meshing with the gear of the rotary damper, for rotating the gear in interlocking fashion with sliding of the locking rod, and in the opposite direction of rotation of the lever.