A mouse includes a main body, an engaging device, and a detachable cover. The main body has a top surface and an insertion slot. The insertion slot is recessed from the top surface of the main body. The cover is used for detachably covering the top surface of the main body. The cover has an extension arm. After the top surface of the main body is covered by the cover, the extension arm is inserted into the insertion slot and engaged with the engaging device, so that the cover is securely fixed on the main body to cover the main body.