A music game apparatus (PC) displays a given game screen according to music piece information. The game screen includes images of performance operators to be operated according to the music piece information. The game apparatus transmits, to an electronic musical apparatus including performance operators, e.g. keys, guide information for providing a performance guide to indicate a particular operator (key) to be operated at timing earlier than timing at which the particular operator should be operated. The musical apparatus provides display to indicate to the user the particular operator to be operated according to the received guide information. The game apparatus may control the musical apparatus to prohibit the performance guide from being carried out according to note information other than the guide information. Further, the game apparatus may control the music apparatus so as to prohibit operation related information representing the operated performance operator from being supplied to a tone generator.