A tappet comprising: a lash adjuster; and a tappet body into which the lash adjuster is inserted and incorporated, wherein the lash adjuster has a plunger having a top portion on which a lower end portion of a push rod is slidable, and a body in which the plunger is housed so as to be vertically movable, and the tappet body has a lower surface portion which slidingly contacts a cam, an outer peripheral surface portion which is slidable on a tappet guide, a receiving surface portion which is located inside the outer peripheral surface portion, receives lubricating oil, and faces upward, an assembly hole which is located inside the outer peripheral surface portion, extends vertically, and has an upper end opened to the receiving surface portion and a lower end closed, and in which the body is inserted and assembled, a receiving space which is located inside the outer peripheral surface portion and opened to an upside of the receiving surface portion, and an oil guide passage which is located at the outer peripheral surface portion or between the outer peripheral surface portion and the assembly hole, and extends so as to guide the lubricating oil received by the receiving surface portion to the cam, characterized in that the oil guide passage has an oil guide groove extending vertically in the outer peripheral surface portion. a lash adjuster; and a tappet body into which the lash adjuster is inserted and incorporated, wherein the lash adjuster has a plunger having a top portion on which a lower end portion of a push rod is slidable, and a body in which the plunger is housed so as to be vertically movable, and the tappet body has a lower surface portion which slidingly contacts a cam, an outer peripheral surface portion which is slidable on a tappet guide, a receiving surface portion which is located inside the outer peripheral surface portion, receives lubricating oil, and faces upward, an assembly hole which is located inside the outer peripheral surface portion, extends vertically, and has an upper end opened to the receiving surface portion and a lower end closed, and in which the body is inserted and assembled, a receiving space which is located inside the outer peripheral surface portion and opened to an upside of the receiving surface portion, and an oil guide passage which is located at the outer peripheral surface portion or between the outer peripheral surface portion and the assembly hole, and extends so as to guide the lubricating oil received by the receiving surface portion to the cam, a lower surface portion which slidingly contacts a cam, an outer peripheral surface portion which is slidable on a tappet guide, a receiving surface portion which is located inside the outer peripheral surface portion, receives lubricating oil, and faces upward, an assembly hole which is located inside the outer peripheral surface portion, extends vertically, and has an upper end opened to the receiving surface portion and a lower end closed, and in which the body is inserted and assembled, a receiving space which is located inside the outer peripheral surface portion and opened to an upside of the receiving surface portion, and an oil guide passage which is located at the outer peripheral surface portion or between the outer peripheral surface portion and the assembly hole, and extends so as to guide the lubricating oil received by the receiving surface portion to the cam, characterized in that the oil guide passage has an oil guide groove extending vertically in the outer peripheral surface portion.