An electronic grand piano comprises a plurality of keys arranged on a keybed, a plurality of actions interlocked with the keys, and an electric circuit unit for performing tone-generation operations based on operations of the actions when the keys are operated. A pair of slide portions, each having an elongated shape, are arranged in parallel and are fixed to outer peripheries of the electric circuit unit. A pair of guide portions are arranged in parallel with respect to a main body of the piano and are loosely engaged with the slide portions. When the electric circuit unit is moved in a prescribed direction relative to the main body, it is automatically stopped and fixed at a prescribed position by means of a fixing structure.