PURPOSE: To make it possible to use a multi-bit data multiplier as plural small number bit data multipliers to be operated at a time by providing the present multiplier with plural decoders installed for a booth of predetermined bits, a carry control circuit for predetermined bits of a 3X generating circuit, and a selector installed as part of a sign bit adding circuit.

CONSTITUTION: The present multiplier is provided with plural decoders Ca5 and Cb5 installed for a booth of predetermined bits, a carry control circuit for predetermined bits of 3X generating circuit, and a selector installed in a part of a sign bit adding circuit. That is, two booth decoders Ca5 and Cb5 are installed for Ya data and Yb data. With this, one multi-bit data multiplier can be used as plural small bit data multipliers to operate small bit data items at a time.