The present invention is intended to provide an agent for treating male infertility which is highly effective to male infertility, and having few side effects. To achieve the object, an agent for treating male infertility comprising δ-amino levulinic acid shown by general formula (1), its derivative or salt thereof: R2R1NCH2COCH2CH2COR3  (1) [wherein R1 and R2 independently represent a hydrogen atom, alkyl group, acyl group, alkoxycarbonyl group, aryl group, or aralkyl group; R3 represents a hydroxy group, alkoxy group, acyloxy group, alkoxycarbonyloxy group, aryloxy group, aralkyloxy group or amino group] can be used.