Disclosed is a catalyst for olefin polymerization comprising nullInull a solid titanium catalyst component nullSnull comprising titanium, magnesium, halogen and an electron donor (b), which is obtained by bringing a solid adduct consisting of a magnesium compound and an electron donor (a) into contact with an electron donor (b) and a liquid titanium compound by at least one method selected from (A) a method of contacting the materials in a suspended state in the coexistence of an inert hydrocarbon solvent and (B) a method of contacting the material plural times individed portions and nullIInull an organometallic compound catalyst component nullMnull containing a metal selected from the groups I to III in the periodic table. By olefin polymerization with this polymerization catalyst, an olefinic (co)polymer having high stereospecificity can be obtained with high activity.