To provide a composite writing instrument which can be reduced in cost, by commonizing a control mechanism for causing each of lower end writing parts of a plurality of writing tools to protrude from a lower end port of a barrel to be unlocked, and then causing the lower end writing parts to withdraw into the lower end port.

The plurality of writing tools each having a thrust lever attached thereto are vertically movably received in the barrel. A lock which can lower in conjunction with the thrust lever of one arbitrarily selected tool is vertically movably received in the barrel. While the lower end writing part of one tool is made to protrude from the lower end port of the barrel, a locking protrusion of the lock which has moved downward together with the thrust lever is made to be capable of locking with a protrusion provided on a clip. After the writing is finished, the clip is elastically deformed to open outward, whereby the locking protrusion is disengaged from the protrusion, and the lock is moved upward by force of a coil spring to allow the lower and writing part of the tool to be withdrawn into the lower end port of the barrel.