A keyboard including a plurality of keys each having a same size and shape and disposed removably and slidably on a frame of the keyboard, the top of each key provided with a marking; a plurality of key switches fixedly mounted on the keyboard frame and each having a predetermined number of movable and fixed contact pairs at predetermined positions; and a plurality of protrusions same in number as the predetermined number and formed at the bottom surface of each key at positions corresponding to the predetermined positions of the contact pairs, the plurality of protrusions being arranged in each key in a different predetermined pattern; whereby when any one of the keys is actuated, the different predetermined pattern of the plurality of protrusions identifies the one of keys, based on a combination of the plurality of protrusions acting upon the predetermined number of contact pairs.