A fuel gas supply device for supplying fuel gas to a fuel cell stack which generates power using the fuel gas and oxidant gas, the fuel gas supply device comprising: a fuel tank storing the fuel gas; a fuel gas path connecting the fuel tank and the fuel cell stack; a control valve provided in the fuel gas path for controlling a supply amount of the fuel gas; an upstream-side pressure sensor for detecting an upstream-side pressure of the fuel gas at an upstream side of the control valve; a downstream-side pressure sensor for detecting a downstream-side pressure of the fuel gas at a downstream side of the control valve; and a programmable controller, wherein no pressure reducing valve is comprised at the upstream side of the control valve in the hydrogen supply path; and the programmable controller is programmed to: calculate a required opening of the control valve based on a target fuel gas pressure in the fuel cell stack and the detected downstream-side pressure and calculate an opening time and a closing time of the control valve based on the required opening and the detected upstream-side pressure; or calculate an opening time and a closing time of the control valve based on the target fuel gas pressure in the fuel cell stack and the detected downstream-side pressure and calculate a required opening of the control valve based on the opening time and the detected upstream-side pressure; and control the control valve using the calculated required opening, opening time and closing time. a fuel tank storing the fuel gas; a fuel gas path connecting the fuel tank and the fuel cell stack; a control valve provided in the fuel gas path for controlling a supply amount of the fuel gas; an upstream-side pressure sensor for detecting an upstream-side pressure of the fuel gas at an upstream side of the control valve; a downstream-side pressure sensor for detecting a downstream-side pressure of the fuel gas at a downstream side of the control valve; and a programmable controller, wherein no pressure reducing valve is comprised at the upstream side of the control valve in the hydrogen supply path; and the programmable controller is programmed to: calculate a required opening of the control valve based on a target fuel gas pressure in the fuel cell stack and the detected downstream-side pressure and calculate an opening time and a closing time of the control valve based on the required opening and the detected upstream-side pressure; or calculate an opening time and a closing time of the control valve based on the target fuel gas pressure in the fuel cell stack and the detected downstream-side pressure and calculate a required opening of the control valve based on the opening time and the detected upstream-side pressure; and control the control valve using the calculated required opening, opening time and closing time. calculate a required opening of the control valve based on a target fuel gas pressure in the fuel cell stack and the detected downstream-side pressure and calculate an opening time and a closing time of the control valve based on the required opening and the detected upstream-side pressure; or calculate an opening time and a closing time of the control valve based on the target fuel gas pressure in the fuel cell stack and the detected downstream-side pressure and calculate a required opening of the control valve based on the opening time and the detected upstream-side pressure; and control the control valve using the calculated required opening, opening time and closing time.