A fuel supply pump includes a pressurizing chamber, a high-pressure path, and a valve unit. The valve unit includes an outlet valve which is configured to open to allow fuel in the pressurizing chamber to flow to the high-pressure path when fuel pressure in the pressurizing chamber becomes higher than a first predetermined pressure. The valve unit also includes a pressure relief valve which is configured to open to allow fuel in the high-pressure path to return to the pressurizing chamber when fuel pressure in the high-pressure path becomes higher than a second predetermined pressure. The valve unit also includes a valve seat member in which a relief path and a plurality of outlet paths are formed, wherein a first end of the relief path opens on a relief valve seat for the pressure relief valve, and respective first ends of the plurality of outlet paths open on an outlet valve seat for the outlet valve.

Embodiments for an internal combustion engine are provided. In one example, and internal combustion engine comprises at least two cylinders each including an injection nozzle and a fuel supply system for supplying the cylinders with fuel. The fuel supply system includes a supply line connecting each injection nozzle to a first fuel reservoir storing fuel at a first pressure, the first fuel reservoir filled by a pump provided upstream, a second fuel reservoir storing fuel at a second pressure less than the first pressure and connected to the first fuel reservoir via a connecting line for filling with fuel, and a bypass line connecting the second fuel reservoir to each injection nozzle. The bypass line opens into the fuel supply system downstream of the first fuel reservoir, thereby forming a connection point, and a shutoff element is arranged in the bypass line, opening or shutting off the bypass line.