A mouse device includes a casing and plural key modules. The plural key modules are installed on two opposite sides of the casing. Each key module includes a switch, an elastic element, a keycap and a stopper. The switch and the elastic element are disposed within the casing. The keycap is detachably connected with the elastic element. The elastic element is arranged between the keycap and the switch. When the keycap is in a pressable state and the keycap is pressed in response to an external force, the keycap is moved in a direction toward the switch and the elastic element is moved with the keycap, so that the switch is triggered by the elastic element. The stopper is detachably connected between the keycap and the elastic element. When the keycap is stopped by the stopper, the keycap is switched from the pressable state to a non-pressable state.