To provide a monomer which is soluble in organic solvents, scarcely contains impurities, gives a polymer having clear thermal phase transition and electric activity, having the basic characteristics, both of liquid crystallinity and electric activity in the same molecule, and excellent performances.

This 2,5-dihalogenothiophene derivative having mesogenic groups at the 3-position and/or the 4-position and used for producing a thiophene polymer having mesogenic groups as side chains is characterized by reacting with a metal selected from the group consisting of magnesium and zinc in the presence of a transition metal compound.