A writing instrument comprising a cylindrical barrel and an end cover attached to a rear end portion of the cylindrical barrel, wherein the end cover comprises: a cylindrical base mounted around the rear end portion of the cylindrical barrel; a cover body fitted around an outer peripheral surface of a rear end portion of the cylindrical base; a stopper ring fitted around an outer peripheral surface of at least a fitted portion of the cylindrical base and the cover body; and a cooperation structure for enhancing a holding force which is exerted on the cover body by the cylindrical base and the stopper ring; the cooperation structure comprising: a first step portion extending radially outward from an outer peripheral surface of a substantially middle portion of the cylindrical base in an axial direction of the cylindrical base; characterized in that the cooperation structure further comprises: an outward facing flange protruding radially outward from a front end portion of the cover body; an engagement portion protruding radially inward from a rear end portion of the stopper ring; and a second step portion extending radially outward from an outer peripheral surface of a portion of the cylindrical base in front of the first step portion; the cover body being fitted around the outer peripheral surface of the rear end portion of the cylindrical base with the outward facing flange being engagedly stopped by the first step portion; and the stopper ring being fitted around the outer peripheral surface of the at least fitted portion of the cylindrical base and the cover body with a front end surface thereof being engagedly stopped by the second step portion, and with the engagement portion being engagedly stopped by a rear end surface of the outward facing flange, and engaged with an outer peripheral surface of the cover body. a cylindrical base mounted around the rear end portion of the cylindrical barrel; a cover body fitted around an outer peripheral surface of a rear end portion of the cylindrical base; a stopper ring fitted around an outer peripheral surface of at least a fitted portion of the cylindrical base and the cover body; and a cooperation structure for enhancing a holding force which is exerted on the cover body by the cylindrical base and the stopper ring; a first step portion extending radially outward from an outer peripheral surface of a substantially middle portion of the cylindrical base in an axial direction of the cylindrical base; an outward facing flange protruding radially outward from a front end portion of the cover body; an engagement portion protruding radially inward from a rear end portion of the stopper ring; and a second step portion extending radially outward from an outer peripheral surface of a portion of the cylindrical base in front of the first step portion; the cover body being fitted around the outer peripheral surface of the rear end portion of the cylindrical base with the outward facing flange being engagedly stopped by the first step portion; and the stopper ring being fitted around the outer peripheral surface of the at least fitted portion of the cylindrical base and the cover body with a front end surface thereof being engagedly stopped by the second step portion, and with the engagement portion being engagedly stopped by a rear end surface of the outward facing flange, and engaged with an outer peripheral surface of the cover body.