A modified conjugated diene-based polymer is produced by reacting a conjugated diene-based polymer having an alkali metal or an alkali-earth metal at a terminal of the polymer with a compound represented by formula (1). R1 and R2 independently represent a hydrocarbyl group having 20 or fewer carbon atoms. R3 represents a substituted alkyl group having 20 or fewer carbon atoms prepared through substitution of at least one of a hydrogen atom and —CH2— of an alkyl group by a group containing only at least one heteroatom selected from the group consisting of nitrogen, phosphorus, oxygen, and sulfur, or a monovalent aromatic group having 20 or fewer carbon atoms and containing at least one element selected from the group consisting of nitrogen, phosphorus, oxygen, and sulfur, with the proviso that R3 does not have active hydrogen. R4 represents an alkanediyl group having 20 or fewer carbon atoms. n is 1 or 2.