Provided is a high-pressure fuel supply pump capable of arranging a relief valve mechanism inside a pump body while suppressing an increase in size and an increase in manufacturing cost. Therefore, a high-pressure fuel supply pump of the present invention includes: a plunger that changes a volume of a pressurizing chamber by reciprocating an inside of a cylinder; a first hole formed from an outer circumferential surface of a pump body toward an inner circumferential side; a relief valve mechanism arranged in the first hole; and a second hole that returns fuel in a flow path on a discharge side of a discharge valve pressurized in the pressurizing chamber to a damper chamber or a plunger seal chamber communicating with the damper chamber when the relief valve mechanism opens in communication with the first hole. At least a part of the relief valve mechanism arranged in the first hole is arranged on the pressurizing chamber side with respect to the uppermost end portion on the pressurizing chamber side of the cylinder.