To make it possible to internally mix plural liquids separately stored in a pump body before a liquid mixture is released by triggering by actuating both a large diameter piston and small diameter piston as an integral body overcoming the force of piston return spring during the compression stroke of the both pistons.

The small-diameter piston 49 is provided with a rod 51. The small-diameter piston 49 and the large-diameter piston 34 are coupled by this rod 51. The piston 49 forms a conical valve skirt 53 overhanging outward toward a piston seal 35. This conical valve skirt 53 slides to limit a mixing chamber 55 while hermetically engaging with the wall of a cylinder 54 during the forward and backward motion of the large-diameter piston 34. Namely, the liquids sucked into the mixing chambers 55, 28 is introduced into the pump chamber 42 during the suction stroke by deforming the conical valve skirt 53 inward in a radial direction. These liquids are mixed with a carrier liquid in this pump chamber and the liquid mixture is simultaneously released from the pump chamber 42 through a release port 43 then through a flow passage 44 from a release hole.