PURPOSE: To accelerate the converting time and at the same time to increase the converting accuracy, by applying the digital data after dividing the data into plural bit groups comprising the same number of bits.

CONSTITUTION: The constant current sources 16 and 17 having different levels of current are connected to the input terminal of an operational amplifier 12 via switches 14 and 15 respectively. The switches 14 and 15 fetch the digital data by the reset signal of a switch 13 and are driven with conduction by counters 18 and 19 which count the digital data by a clock signal. The counter 18 feeds the data of upper 8 bits among the digital data to be converted and counts the clocks for a period of the data value shown by the upper 8 bits to make the switch 14 turned on for driving. While the counter 19 feeds the data of lower 8 bits and counts the clocks for a period of the data value shown by the lower 8 bits to make the switch 15 turned on for driving.