Peptide derivatives represented by the general formula (1) have smooth muscle contracting effect. (1) [In the formula, n is an integer of 0 to 6; Ar is an aromatic ring which may have one or more substituents or be fused with another ring; R1 is linear or branched lower alkyl which may be substituted; R2 is linear or branched lower alkyl which may be substituted; R3 is linear or branched lower alkyl which may be substituted; and X is amino, hydroxyl, or lower alkoxy.]
