In order to realize a small and light key actuating apparatus for actuating a key which is rotatably supported with respect to a frame, a key actuating apparatus (7) is provided which includes a polymer transducer (9) for rotatably moving the key (3) by using a deformation of the transducer, wherein the transducer which is substantially formed in a plate shape includes: a polymer film (15) which is dielectric and made from an elastically deformable polymer material; and a pair of electrodes (17) arranged at both sides of surfaces of the polymer film, and the transducer is deformed corresponding to switching between an application of voltage and a lack of voltage between the electrodes.