The invention is directed to a fuel injection pump for a two-stroke engine mounted in a work apparatus such as a motor-driven chain saw. The injection pump includes a pneumatic drive chamber which is charged with the crankcase pressure of the two-stroke engine. A membrane mounted in the drive chamber transmits the pulses of the crankcase pressure to a pump piston which moves into a pump chamber against the force of a leaf spring. The leaf spring is configured as a leaf spring packet of individual leaf springs in order to obtain an adaptation of the injected fuel quantity to the position of the throttle flap of the engine.