An arrangement for controlling the fuel supply in a fuel supply apparatus, which arrangement comprises a body part including a space, through which the fuel to be injected flows during the operation, and a fuel inlet opening and a fuel discharge opening, which open into said space, the arrangement further comprising a piston member movably arranged in said space and a flow path to provide flow communication between the fuel inlet opening and the fuel discharge opening. The arrangement comprises at least one throttle section opening to the front of the piston member in the flow direction of the fuel, the cross-sectional flow area of which section is determined by the mutual positions of the piston member and the body part.