To provide a common-rail fuel supply device usable in common for an engine different in the number of cylinders.

Fuel is force-fed to a common rail 3 connected to fuel injection- valves 1 of an internal combustion engine 10, using an inner cam type high pressure fuel feed pump 5. The inner cam shape and cylinder layout of the pump 5 are so constituted as to make the total of discharge from each cylinder constant throughout the operating cycle of the pump 5. A force-feed control valve is provided at a force-feed passage connecting the discharge port of each cylinder of the pump 5 to the common rail, and the force-feed control valve is opened/closed every fuel injection from the fuel injection valves 1 to force-feed fuel to the common rail. Since the total of discharge from each cylinder of the pump 5 is constant throughout the operating cycle of the pump 5, fuel can be force-fed to the common rail even at the time other than force-feed stroke timing of each cylinder, and the same pump 5 can be used in common for an engine different in the number of cylinders.