A device for detecting micro particles in gas, which comprises: an inlet through which a gaseous sample including micro particles flows in; an outlet through which the sample flows out; a channel through which the sample flows from the inlet toward the outlet; a cooling layer which cools and condenses the sample flowing in the channel; a reservoir which is positioned on the cooling layer and collects the condensed sample; a detector which is positioned in the reservoir on the cooling layer and detects the micro particles included in the collected sample; and a heater which heats the outlet portion to produce a pressure difference between the inlet portion and the outlet portion, so that the sample flows through the channel from the inlet toward the outlet. The device for detecting micro particles in gas provides the advantage that micro particles included in gaseous sample can be detected without having to use additional pump or collector, detection time can be reduced, and detection accuracy can be improved.