Fuel injection pump of the type arranged to inject fuel into engine cylinders with the fuel flow being controlled by an electromagnetic valve, comprises a rotor arranged to rotate in timed relation to engine rotation, and a shuttle movably received in an axial bore made in the rotor. Opposite sides of the shuttle define first and second chambers within the axial bore, where the first chamber is used as a compression chamber to pressurize fuel introduced therein via the electromagnetic valve to inject the same into engine cylinders, and the second chamber is communicable with a low pressure fuel reservoir. Fuel is fed into the first and second chambers during an intake stroke or mode, and then the second chamber fuel is pressurized by means of an inner cam mechanism so that the shuttle moves toward the first chamber to pressurize the fuel therein, thereby injecting the fuel during a compression stroke. When the shuttle has been moved toward the first chamber beyond a predetermined position, the second chamber communicates with the low pressure fuel reservoir via a by-pass, lowering fuel pressure in the second chamber to terminate injection. The amount of fuel injected into cylinders is controlled by the stroke of the shuttle toward the first chamber, which stroke is initially determined by the energizing interval of the electromagnetic valve.