To provide a mass flow control device arranged to perform an official approval operation of a mass flow in the device itself by incorporating a tank for the official approval.

The mass flow control device comprises a mass flow detection means 8 for detecting the mass flow of a fluid flowing through a channel 6 feeding the fluid and outputting a mass flow signal; a flow control valve mechanism 10 for controlling the mass flow by varying the valve opening by a valve drive signal; and a control means 18 for controlling the flow control valve mechanism based on an externally input flow setting signal and the flow signal. The flow control is provided in the channel with a valve part 42 for the official approval for opening/closing the channel, the tank part 44 for the official approval having a specified tank capacity and a pressure detection means 46 detecting the fluid pressure and outputting the pressure detection signal. An official approval control means 48 controls the official approval operation of the mass flow to be carried out using the valve for the official approval, the tank part for the official approval and the pressure detection means.