To certainly prevent an inconvenience such as the occurrence of a rust in a component of a lock mechanism; entering of a stain adhering to the surface of a door together with rust; freezing of an entering water in a winter to turn the components of the lock mechanism into a state of impossible action and release of lock by surely preventing the water from entering into the lock mechanism of the door of an automobile.

A key inserting mouth 3a of a lock mechanism 3 is arranged near a door opening handle 2, and a cover part 9 covers the key inserting mouth 3a in the nonoperating state of the door opening handle 2. The key inserting mouth 3a is arranged on the front side of a casing 1, and the cover part 9 is longitudinally and protrusively provided in the lower part on one side of an opening operation part 7, or the key inserting mouth 3a is provided inside the side part of the casing 1, and the cover part 9 is provided on the handle 2 so as to lengthen in the direction of an opening operation inside the casing 1.