A keyboard including an upper casing which has a key-holder member for movably supporting keys with a movable electrode, and a lower casing which has an integrally formed upraised portion which defines a recess open in the bottom wall of the lower casing. A printed-circuit board is held in direct contact with the top wall of the upraised portion of the lower casing such that stationary electrodes on the printed-circuit board are opposite to the corresponding movable electrodes. The printed-circuit board may be a flexible film-like member on which an elastic sheet having elastically collapsible cap portions is disposed such that the cap portions cooperate with the film-like printed-circuit board to form enclosures in which the corresponding movable and stationary electrodes are accommodated, and such that the cap portions collapse upon operation of the keys for moving of the movable electrodes toward the stationary electrodes. The film-like board has an air vent communicating with each enclosure, while the top wall of the upraised portion of the lower casing has a groove communicating with the air vent, so that the air in the enclosure may flow into the groove through the air vent upon collapse of the cap portion.