In this paper, we propose a flash type A/D (Analog-to-Digital) converter. This circuit uses a neuron CMOS inverter as a judgement component of the voltage level. It is smaller than traditional analog comparators in the power consumption and the layout area. Therefore, the power consumption and the layout area of this circuit can be reduced further compared with the conventional A/D converter using the analog comparator. Furthermore, we could confirm that the proposed circuit has a characteristic of high-speed operation.