In a music reproducing apparatus, a timbre data memory has a limited capacity for storing timbre data corresponding to a first number of timbres, which is less than a second number of timbres reserved in a data source. An interface can be operated to transfer the timbre data from the data source to the timbre data memory so that the timbre data memory stores the transferred timbre data. A score data memory stores score data representing a music piece. A tone generator is set with a tone generating parameter derived from the score data stored in the score data memory for generating tones of the music piece. A performance controller interprets the score data to read out timbre data designated by the score data from the timbre data memory for setting the tone generator with the read timbre data so that the tone generator can generate the tones having timbres specified by the score data. Further, a memory monitor detects when a vacant area is created in a limited space of the score data memory upon sequential retrieval of the score data for operating the interface to load another part of the score data into the vacant area, thereby enabling the tone generator to continue the generating of the tones of the music piece.