The present invention provides a sound source controlling device in which the processing load required for interpretation of music data may be varied, depending upon the CPU load. The interval of music data interpretation is changed, without changing the music data itself, and the reproduced music composition is not changed in tempo. A system load judgment unit 152 compares the system load information acquired by a system load information acquisition unit 151, with a threshold value stored in a system load threshold value holding unit 153, and accordingly selects a timer interrupt interval held by a timer interrupt interval holder 131. A time information supervisor 143 supervises the acquisition of music paper data held by a music paper data holder, responsive to the timer interrupt interval held by an internal resolution holder 145. A sound enunciation/sound erasure information controller 144 controls a sound source based upon the acquired music paper data.