A computer portion 70 determines main reaction force RF0 by use of a main reaction force table storing main reaction forces which vary according to the velocity and the depth of a depression of the key 11. The computer portion 70 determines first ancillary reaction force RF1 by use of a first ancillary reaction force table storing first ancillary reaction forces which vary according to the amount of depression of a lever 32 of a pedal apparatus 30. The computer portion 70 adds the first ancillary reaction force RF1 to the main reaction force RF0 to obtain a composite reaction force to control a solenoid 21 on the basis of the composite reaction force so that a reaction force which is to be exerted on the key 11 will be the composite reaction force.