A plunger for a syringe of a liquid dispenser comprises a tapered front end section 12 having at its rear end 16 an outer diameter slightly smaller than the inner diameter of the syringe, a cylindrical drum section 14 continued to the rear end 16 of the tapered front end section 12, having a maximum outer diameter substantially the same as the inner diameter of the syringe and opening there, and a collar member 24 (30, 32) slidably formed by coupling with an outer circumferential surface in the vicinity of an opening 22 of the drum section 14 and maintaining the close contact with an inner wall surface 26 of the syringe 18, thereby inclination toward the syringe is eliminated and action within the syringe is constantly made smooth.