To provide a liquid mixer for mixing the minute quantity of liquid which has improved mixing efficiency per plate to be suitable even to the mixing of the minute quantity of liquid.

A plate 20 is superimposed on a plate 2 in a liquid tight way in such a manner that the half-etched part 4a of the plate 2 is located on the side of the plate 20. Other plates are superimposed in a liquid tight way so as to hold the two plates 2 and 20, and joining is performed so as to seal the holes of the plates 2 and 20 excepting a liquid inlet 18 and a liquid outlet 10 on the lowermost stream. A liquid and B liquid fed from the liquid inlet 18 enter the central parts of the holes 22 and 24 of the plate 20, are distributed toward the edge parts of each of the holes 22 and 24, and are fed to a hole 4b sequentially to form the flows of four layers in the depth direction of a groove. The flows flow to the downstream side, are mutually diffused in the middle of the flowing so as to be mixed. The flow passes through the part 4a to promote the mixing, reaches a hole 4c, is fed from the part of the hole 4c to the central part of the hole 22 or 24 in the plate 20 again, and is distributed to two or four again.