<p>In a high pressure fuel supply pump for transmitting rotation of a cam 7 to a reciprocating plunger 2 via a tappet 6 and a retainer 3, a diametric force acting on the plunger 2 is reduced. The high pressure fuel supply pump includes the retainer 3 disposed on the plunger 2 and a return spring 4 exerting an urging force on the retainer 3 in a direction of the tappet 6. A clearance between a plunger leading end 201 and a tappet bottom surface 601 opposed thereto is set to be greater than a clearance between a retainer bottom surface 301 and the tappet bottom surface 602 opposed thereto, and a clearance between a retainer inside diameter section 302 and a plunger peripheral surface section 203 opposed thereto is set to be greater than a clearance between a retainer outside diameter section 303 and a tappet inner wall 603 opposed thereto. The foregoing arrangements make a plunger diametric force involved in flexural deformation or shear deformation of the spring 4 less easy to be transmitted to the plunger 2. As a result, a fault of the plunger 2 galling a cylinder inner wall 2A can be reduced.
</p>
