In normal mode or expansion mode, a normal load table 53 or an expansion load table 54 is selected, respectively, to store half area start position HS and half area end position HE as effect-switchable positions. The selected load table is referenced to generate and output drive signals so as to obtain depression reaction force F according to position ST. In accordance with player's depression/release of keys, musical tone signals are generated on the basis of waveform data 51 and envelope data 52 corresponding to the manipulated keys, designated basic tone color and depression area to carry out tone emission/tone-vanishing processes. Both the characteristics of musical tones and the rate of change in the reaction force switch at the effect-switchable positions.