To provide a mass flow controller capable of performing test operation of a mass flow rate by the device itself by incorporating a test tank.

This mass flow controller comprises a control means 18 for controlling a flow control valve mechanism based on an externally input flow set signal and a flow signal, wherein a mass flow detector means 8 for detecting the mass flow rate of the fluid flowing through a channel and outputting a flow signal and the flow control valve mechanism 10 for controlling the mass flow rate by altering the valve aperture by means of valve drive signals are interposed in the channel 6 through which the fluid flows. The mass flow control device has a constitution equipped with a test control means 48 for controlling a test valve part, a test tank part and a pressure detector means to carry out the mass flow test operations, which is provided respectively in the channel with the test valve part 42 for opening and closing the channel, the test tank part 44 having a prescribed volume, and the pressure detector means 46 for detecting the pressure of the fluid and outputting pressure detection signals.