A high pressure fuel supply apparatus 6 has a plunger 161 reciprocating and sliding in a sleeve 160 of a high pressure fuel pump 16 to form a fuel pressurizing chamber 163 between the plunger 161 and the sleeve 160 to discharge pressurized fuel; a bolt 180 forming a part of a housing of the high pressure fuel pump 16; and an oil seal 169 fixed to an inner wall surface of the bolt 180 by press fitting to slide on an outer circumferential wall of the plunger 161 in accordance with reciprocating motion of the plunger 161 to seal the fuel and lubricating oil; wherein the bolt 180 is formed so that a press-in load in a second half of a press-in stroke of the seal 169 is higher than that in a first half thereof in an abutment portion of the bolt 180 against the seal 169.