PURPOSE: To obtain a fine free flowable granular coordination polymerization polymer containing no largely contaminated agglomerates from a coordination polymerizable monomer by using a reactor not substantially containing a dead space during polymerization and receiving mechanical wiping-off action during polymerization by its whole inner surface being in contact with reaction content.

CONSTITUTION: A coordination polymerizable monomer is brought into contact with a coordination polymerization catalyst under a coordination polymerization condition within a reactor having no dead space under a reaction condition and receiving mechanical wiping-off action by its total surface being contact with reaction content to perform polymerization for a time sufficient to form a granular solid polymer. As the reactor, a twin-screw reactor having surface wiping-off action is pref. used. As the coordination polymerizable monomer, styrene, a styrene derivative, ethylene, propylene or butene are designated. The coordination polymerization catalyst is prepared from a transition metal compd. and to polyalkylaluminoxane.