Fuel supply device for internal combustion engine

A fuel supply device for an internal combustion engine includes a tank, a fuel injection valve, a fuel passage, a second shut-off valve to open and close the fuel passage, a variable volume mechanism configured to vary the volume of a downstream-side fuel passage, which is a section of the fuel passage that is connected to a downstream side of the electromagnetic valve, and a controller that executes a fuel pressure control. In the fuel pressure control, the second shut-off valve is repeatedly opened and closed such that the fuel pressure in the downstream-side fuel passage falls within a range defined by an upper limit value and a lower limit value. The controller executes a volume increasing process that operates the variable volume mechanism to increase the volume of the downstream-side fuel passage during the execution of the fuel pressure control.