Fuel supply device

A fuel supply device, comprising:

• a fuel injection valve configured to inject gas fuel;
• a delivery pipe that supplies the gas fuel to the fuel injection valve;
• a relief passage that connects an intake passage of an internal combustion engine and the delivery pipe;
• a first valve configured to open so that the gas fuel in the delivery pipe is supplied to the relief passage;
• and
• a second valve arranged in the relief passage, wherein:
• the delivery pipe, the first valve, the second valve, and the intake passage are arranged in this order;
• and
• a downstream pressure refers to a pressure of the relief passage at a side of the second valve toward the intake passage,
• an upstream pressure refers to a pressure of the relief passage at a side of the second valve toward the delivery pipe,
• the second valve includes a body, a valve member configured to close an opening in the body, and a spring that presses the valve member against the opening of the body,
• the second valve is configured to open in response to the downstream pressure becoming lower than the upstream pressure by an amount that is greater than a pressing force of the spring that presses the valve member against the opening of the body, and
• in response to the second valve opening, the gas fuel upstream from the second valve flows into the intake passage.