Preferred embodiments include a jack holder 48 that is free to swing in accordance with the depression operation of a key 10, a first elastic member 52 that impels the jack holder 48 and applies the first counter force to the key 10 against the key depression action, the jack 42 that, together with being established so that it is not possible for it to swing with respect to the jack holder 48 during the depression operation of the key 10, is also established so that it is free to swing with respect to the jack holder 48 during the releasing operation of the key 10 and the second elastic member 56 that impels the jack 42 and applies the second counter force, which is smaller than the first counter force, to the key 10 against the key releasing action.