To reduce a device cost, in a fuel supply device supplying gaseous fuel and liquid fuel to an internal combustion engine.

The fuel supply device includes: a gaseous fuel supply path 35 supplying the gaseous fuel to a gas phase part 13 of a liquid fuel tank 5; a second pressure sensor 41 detecting gas phase pressure of the liquid fuel tank 5; a third pressure regulating valve 39 regulating pressure of the gaseous fuel flowing toward the gas phase part 13; and an ECU controlling the gas phase pressure of the liquid fuel tank 5 by using the third pressure regulating valve 39 as an operation end. The gas phase pressure of the liquid fuel tank 5 pressurizes the liquid fuel constituting the liquid phase part 12 to feed the liquid fuel into a fuel injection pump. Since the need of a feed pump required to transport the liquid fuel from the liquid fuel tank 5 to the fuel injection pump is eliminated, the device cost can be reduced.