PURPOSE: To obtain a hydraulic cement mixture large in slump value by forming a water reducing agent layer on the surface part of a spherical cement.

CONSTITUTION: Cement clinker particles in a hopper 14 are supplied to a ring- like collision chamber 7 through a cement chute 13, brought into contact with a rotary disk 4 rotating at the rotating speed of 4000-16000rpm and a blade 5 attached thereto, scattered in high speed gas flow while revolving at a high speed in the chamber 7 and made to collide with the surface of a ring-like stators 8 and the blade 5 while revolving. At the same time, the powdery water reducing agent is fed and the resultant mixture is finely pulverized into spherical shape by circulating it in the collision chamber 7 through a circulating circuit pipe 12 for 3-20min and after that, is taken out from a chute 11 with a discharge valve 10 opened and a cement particle 20a layer and the water reducing agent layer 21 are formed on the surface of the cement base particle 20.