PURPOSE: To make it possible to read a random signal of a random part in mass ROM freely with simple constitution by reading each ROM of composite ROM stored in common addresses forming a fixed no-signal part according to assignment.

CONSTITUTION: Through the operation of keyboard 5, the low-order two bits, etc., of ROMs 1AW1D of composite ROM4 are assigned for the initial address of the 2nd music, etc., of fixed bits of a no-signal component and that of the 3rd music, etc. Then, every time the initial address changes to one bit according to the clock counting-up of the program counter of control part 6 and the low-order two bits, etc., reach 00, ROMs 1AW1D are read and the contents of the 2nd music, etc., are read sequentially and continuously until the initial address of the 3rd music, etc., latched according to the operation of board 5 agrees with the count value of the program counter. Therefore, the simple constitution can read a random signal at a random part in mass storage ROM freely.