An electronic musical instrument allows a player to operate operators as least number of times as possible to play music, and the player can play music easily and agreeably, using the instrument. Every measure decided by plural beats counted based on a designated meter a prior tone is determined from among automatic playing music data. The prior tone is a musical tone which is made note-on for example at a timing of a downbeat in the measure. If a candidate for the prior tone is one of chord composing tones, and the one of chord composing tones can compose a melody, then such musical tone is decided as the prior tone. The prior tones successively decided from the beginning of the automatic playing music data are indicated to the player as lighted up keys. The player operates the lighted up keys successively to perform the automatic playing music data.