A vehicle seat reclining apparatus comprising: a base member which is to be connected to one of a seat cushion and a seat back connected rotatably with the seat cushion; a rotation member which is to be connected to the other of the seat cushion and the seat back, which is arranged to rotate relative to the base member and which includes an internal gear; a regulating member to regulate axial movement of the rotation member relative to the base member; a lock tooth member which includes an external gear capable of engaging with the internal gear and which is arranged to move between a lock position at which the external gear engages with the internal gear of the rotation member and an unlock position at which the external gear disengages from the internal gear; and a cam arranged to push the lock tooth member to move the lock tooth member between the lock position and the unlock position; wherein the base member includes an outer circumferential portion defining a circular recess, the rotation member includes an outer circumferential portion including a cylindrical portion which is fit rotatably in the outer circumferential portion of the base member, and which includes an inside circumferential surface formed with the internal gear, the cylindrical portion of the rotation member further includes a sliding outside cylindrical surface to limit radial movement of the rotation member relative to the base member by being fit slidably in an inside cylindrical surface of the outer circumferential portion of the base member, and wherein the outer circumferential portion of the rotation member further includes a flange portion which projects radially outwards from the cylindrical portion, which is placed axially between the regulating member and the outer circumferential portion of the base member and which includes a side surface facing away from the base member and serving as the sliding regulation surface; characterized in that the cylindrical portion of the rotation member further includes a first side surface facing toward the base member and a second side surface facing away from the base member and serving as sliding regulation surface facing axially to the regulating member and being in sliding contact with the regulating member. a base member which is to be connected to one of a seat cushion and a seat back connected rotatably with the seat cushion; a rotation member which is to be connected to the other of the seat cushion and the seat back, which is arranged to rotate relative to the base member and which includes an internal gear; a regulating member to regulate axial movement of the rotation member relative to the base member; a lock tooth member which includes an external gear capable of engaging with the internal gear and which is arranged to move between a lock position at which the external gear engages with the internal gear of the rotation member and an unlock position at which the external gear disengages from the internal gear; and a cam arranged to push the lock tooth member to move the lock tooth member between the lock position and the unlock position; wherein the base member includes an outer circumferential portion defining a circular recess, the rotation member includes an outer circumferential portion including a cylindrical portion which is fit rotatably in the outer circumferential portion of the base member, and which includes an inside circumferential surface formed with the internal gear, the cylindrical portion of the rotation member further includes a sliding outside cylindrical surface to limit radial movement of the rotation member relative to the base member by being fit slidably in an inside cylindrical surface of the outer circumferential portion of the base member, and wherein the outer circumferential portion of the rotation member further includes a flange portion which projects radially outwards from the cylindrical portion, which is placed axially between the regulating member and the outer circumferential portion of the base member and which includes a side surface facing away from the base member and serving as the sliding regulation surface; characterized in that the cylindrical portion of the rotation member further includes a first side surface facing toward the base member and a second side surface facing away from the base member and serving as sliding regulation surface facing axially to the regulating member and being in sliding contact with the regulating member.