A magnesium compound obtained by reacting metallic magnesium having a sphericity (S) of less than 4.00, the sphericity (S) being represented by the following formula (I), an alcohol, and a halogen and/or a halogen-containing compound containing halogen atoms in an amount of 0.0001 gram atom or more relative to one gram atom of the metallic magnesium, S=(L.sub.1/L.sub.2).sup.3 (I) wherein L.sub.1 represents the maximum diameter of projection views of metallic magnesium determined by photographing with a scanning electron microscope and thereafter an image processing, and L.sub.2 represents a diameter of a circle having an area equal to the area of the projection view of metallic magnesium. A solid catalyst component is obtained from the magnesium compound and a titanium compound, and a catalyst for olefin polymerization is obtained using the solid catalyst component.