There have been proposed many processes for the production of a solid catalyst component for the polymerization of olefins which is composed essentially of magnesium, titanium, halogen, and an electron donor compound.  The catalyst component produced by these processes has made it possible to produce in high yields polymers having considerably high stereoregularity.  However, there still exists a demand for further improvement. 
In the production of olefin polymers, it is important to regulate the particle shape of the polymer obtained.  Recently, there has been proposed several methods for producing in high yields olefin polymers which have high stereoregularity and improved particle properties.  For example, there is disclosed in U.S. Pat.  No.  4,330,649 a process for producing an olefin polymer by using a catalyst component which is obtained by contacting a liquid magnesium compound having no reducing ability, a liquid titanium compound, and an electron donor compound having no active hydrogen with one another in the liquid state.  This process has an advantage over the conventional technology; yet it is not satisfactory. 
There is disclosed in Japanese Patent Laid-open No.  92009/1982 a catalyst component for the polymerization of olefins which is produced by contacting a magnesium compound, an electron donor compound, a silicon compound having the Si-H bond, and a titanium halide with one another.  The magnesium compound used in the disclosed invention is substantially insoluble in an inert solvent; therefore, it is impossible to contact the magnesium compound with an electron donor compound and/or silicon compound in the liquid state.  Thus the resulting catalyst component is low in catalytic activity and provides a polymer having low stereoregularity and unsatisfactory particle properties. 
There is disclosed in Japanese Patent Laid-open No.  36203/1980 a catalyst component which is produced by contacting a hydrocarbon-soluble organomagnesium component or a reaction product thereof with a complex, with a chlorosilane compound having the Si-H bond, and contacting the resulting solid with a titanium compound and an ester of carboxylic acid.  The solid has the Mg-C bond having reducing ability, which is not formed when a magnesium dialkoxide is used in the present invention.  The resulting catalyst component has low catalytic activity and provides polymers having unsatisfactory particle properties.