High-Pressure Fuel Supply Pump

An object of the present invention is to provide a high-pressure fuel supply pump that can restrict lowering of pressure and generation of cavitation in the vicinity of a seat by providing a throttle in a relief spring holder. Accordingly, in order to achieve the above object, the present invention relates to a fuel supply pump that includes a pressurizing chamber configured to pressurize fuel, and a relief valve mechanism configured to return fuel in a discharge path on a downstream side of the discharge valve to the pressurizing chamber. The relief valve mechanism includes a relief seat configured to close a relief channel when a relief valve is seated, a relief spring configured to energize the relief valve to the relief seat, and a relief spring holder configured to hold the relief spring. In the relief spring holder, a throttle section is formed in a fuel path for returning from a relief chamber in which the relief spring is disposed to the pressurizing chamber and the channel. The above object can be achieved by the above configuration.