A differential-pressure flow meter is capable of easily eliminating adhesion to an orifice of an extraneous material. The differential-pressure flow meter includes: a pair of pressure sensors provided on a straight pipe part of a main fluid channel; an orifice unit interposed between the pair of pressure sensors; a columnar orifice body provided on the main fluid channel to be detachable in a direction orthogonal to a flow direction of a fluid in the main fluid channel; and an orifice hole penetrating the orifice body in the flow direction of the fluid, wherein the orifice body is rotatable at a prescribed installation position to reverse an upstream side and a downstream side with respect to the orifice hole, and flow rate measurement is performed by converting into a flow rate a difference in pressure that is obtained from two pressure values sensed respectively by the pair of pressure sensors.