Abstract: A reaction gas supplying comprising an MFC and adapted to sense when there is an error in the MFC, and a related method are disclosed. The reaction gas supplying device comprises a gas supply line disposed between a process chamber and a gas supplying element, a mass flow controller adapted to control a supply amount and a supply time of a gas, and a digital pressure gauge adapted to measure the pressure of the gas. The device further comprises a database, and a controller adapted to generate and output a first flow rate control signal, compare the measured pressure value of the gas with a standard pressure value stored in the database corresponding to the first flow rate control signal, and output an alarm generation control signal when the measured pressure value of the gas is outside of a set error range around the standard pressure value.