A key top attachment structure which makes the key-top attachment work easy, prevents the key top from being taken off from the outside, and suppresses looseness of the key top. A spring (11) provided with a rectangular hole (14), and lock portions (12A, 12B and 13) in which corresponding stoppers (22A, 22B and 23) of a key top (2) are to be locked respectively, are provided in a casing (1) of a small-sized electronic equipment such as an inter-call receiver or the like. A protrusion (21) which pushes the spring (11) at the time of attachment, a protrusion (24) which abuts against the spring (11) after attachment, a protrusion (25) which turns on a switch (3) on a printed board (4), and the stoppers (22A, 22B and 23) are provided in the key top (2).