A fuel supply pump comprising: a pump housing (11, 111, 211, 311); a cylinder head (12, 112, 212, 312) that is fitted to a cylinder hole (11a, 111a, 211a, 311a) formed in the pump housing (11, 111, 211, 311); a plunger (13, 313) that is slidably fitted to a sliding hole (12a, 212a, 312a) formed in the cylinder head (12, 112, 212, 312); a tappet (18, 118, 218, 318, 518) that is slidably fitted to the cylinder hole (11a, 111a, 211a, 311a); a cam shaft that is rotatably supported in a cam chamber formed inside the pump housing (11, 111, 211, 311) so as to communicate with the cylinder hole (11a, 111a, 211a, 311a); a cam that is formed integrally with the cam shaft; and a plunger spring (15, 215, 315) that is interposed between the cylinder head (12, 112, 212, 312) and the tappet (18, 118, 218, 318, 518), wherein the tappet (18, 118, 218, 318, 518) is configured to have a cylindrical tappet body (16, 116, 216, 316) and a roller (17, 117, 217, 317), wherein a cylindrical guide ring (26, 126, 226, 326, 526) is fixed into the cylinder hole (11a, 111a, 211a, 311a), and wherein in the tappet body (16, 116, 216, 316) and a cylindrical portion of the guide ring (26, 126, 226, 326, 526), a tappet side guide portion (16a, 116a, 216a, 316a, 516a) and a guide ring side guide portion (26a, 126a, 226a, 326a, 526a) which can be fitted thereto in an axial direction are provided in at least two locations; characterized in that the tappet side guide portion (16a, 116a, 216a, 316a, 516a) and the guide ring side guide portion (26a, 126a, 226a, 326a, 526a) are provided in at least two locations at equal intervals; wherein either the guide ring side guide portion (26a, 126a, 226a, 326a) has a convex protruding shape and the tappet side guide portion (16a, 116a, 216a, 316a) has a concave cut-out shape or the guide ring side guide portion has a concave cut-out shape and the tappet side guide portion has a convex protruding shape; and wherein a depth of the cut-out portion and a length of the protruding portion are configured to be longer than a pumping stroke of the fuel supply pump. a pump housing (11, 111, 211, 311); a cylinder head (12, 112, 212, 312) that is fitted to a cylinder hole (11a, 111a, 211a, 311a) formed in the pump housing (11, 111, 211, 311); a plunger (13, 313) that is slidably fitted to a sliding hole (12a, 212a, 312a) formed in the cylinder head (12, 112, 212, 312); a tappet (18, 118, 218, 318, 518) that is slidably fitted to the cylinder hole (11a, 111a, 211a, 311a); a cam shaft that is rotatably supported in a cam chamber formed inside the pump housing (11, 111, 211, 311) so as to communicate with the cylinder hole (11a, 111a, 211a, 311a); a cam that is formed integrally with the cam shaft; and a plunger spring (15, 215, 315) that is interposed between the cylinder head (12, 112, 212, 312) and the tappet (18, 118, 218, 318, 518), wherein the tappet (18, 118, 218, 318, 518) is configured to have a cylindrical tappet body (16, 116, 216, 316) and a roller (17, 117, 217, 317), wherein a cylindrical guide ring (26, 126, 226, 326, 526) is fixed into the cylinder hole (11a, 111a, 211a, 311a), and wherein in the tappet body (16, 116, 216, 316) and a cylindrical portion of the guide ring (26, 126, 226, 326, 526), a tappet side guide portion (16a, 116a, 216a, 316a, 516a) and a guide ring side guide portion (26a, 126a, 226a, 326a, 526a) which can be fitted thereto in an axial direction are provided in at least two locations; characterized in that the tappet side guide portion (16a, 116a, 216a, 316a, 516a) and the guide ring side guide portion (26a, 126a, 226a, 326a, 526a) are provided in at least two locations at equal intervals; wherein either the guide ring side guide portion (26a, 126a, 226a, 326a) has a convex protruding shape and the tappet side guide portion (16a, 116a, 216a, 316a) has a concave cut-out shape or the guide ring side guide portion has a concave cut-out shape and the tappet side guide portion has a convex protruding shape; and wherein a depth of the cut-out portion and a length of the protruding portion are configured to be longer than a pumping stroke of the fuel supply pump.