PURPOSE: To obtain a waterproof device which can be operated with a force similar to the force required for a general camera, by forming a waterproof packing into a hollow shape and charging a fluid into the packing and making the pressure of the fluid at the cover closing time different from that after closing of the cover.

CONSTITUTION: When a rear cover is opened, power is supplied to a coil 11 by a signal from a switch 1j, and a solenoid valve 8 is moved right in the figure. An exhaust port 6b is opened, and air in a packing tube 3 is connected to the external; and therefore, if the rear cover is pushed from the rear when the rear cover is closed after film loading, the packing tube is pushed by a projecting edge part 2b and is easily crushed, and a claw 2c pushes the outside inclining part of a lock claw 4a in the camera side to push it down against a spring 5, and the claw 4a is restored upward when the claw 2c gets over the claw 4a, and the rear cover is locked. When a notched gear 19 is rotated in the direction of an arrow, a piston 17 compresses air in a cylinder 14, and compressed air is sent into the packing tube 3 through tubes 12a and 6a.