To obtain foaming with an appropriate mixing ratio from the beginning of pump operation by making inflow of air ahead of a liq. in inflow of air and the liq. into a mixing room and to avoid changes of color and properties of a stored liq. caused by rusting of a coil spring for energizing upward a working member.

Under the condition where a coil spring 35 is put in a large diameter cylinder 4 for air compression and a working member 30 is positioned at the upper limit, a gap between a stem fitting cylinder 39 of a head 37 and the second outerward facing flange-like wall 45 of the large diameter piston 42 is made smaller than a gap between a suction valve body 82 at the lower end of a rod-like member 80 and a suction valve seat 13 on the bottom part of a small diameter cylinder 5. When the head 37 is pushed down, pushing down of the large diameter piston 42 by means of the stem fitting cylinder 39 is made thereby faster than closing of a valve formed by the suction valve body 82 and the suction valve seat 13 to make inflow of air into a mixing room 57 faster than inflow of a liq. into the mixing room.