A lock includes a main body, a shining device, and a switch; the main body has a holding portion on one side thereof, which is formed with a through hole; the shining device is held in the holding portion of the main body, and it includes a power source, and a light emitting element; the light emitting element is held in the through hole of the holding portion of the main body such that light emitted from it will travel outside the main body; the switch is connected to the shining device for turning on/off the power for the light emitting element.