To provide a reliable pump which can control a flow rate with a simple structure at a reasonable cost.

By referring to a current value-exhaust flow rate relationship (4,000 rpm) 64 stored in a judgment reference storage means 6, an exhaust flow rate is calculated from a detected current value obtained by a current value detection means 3. A flow rate judging unit 53 judges whether the obtained exhaust flow rate is a predetermined set flow rate (10L/min). According to the result of the judgment, the rpm of a motor is controlled so as to control the exhaust flow rate. Accordingly, there is no need of expensive parts such as a flowmeter or a pressure detector which have been conventionally required. Thus, it is possible to control a flow rate with a simple structure at a reasonable cost. Furthermore, since no flowmeter or no pressure detector is used, there is no risk of a pump failure caused by clogging of a flowmeter or a pressure detector with foreign matters. That is, it is possible to perform a highly reliable flow rate control.