A resin composition includes a polyester capable of forming a crystal structure, and a substance represented by the following general structural formula (1), the substance represented by the following general structural formula (1) has a dehydration-condensed structure of two molecules of natural product-derived α-amino acids or a substitution structure thereof, and the two molecules of α-amino acids are not simultaneously glycine. In the above general structural formula, R1, R2, R3, and R4 indicate groups or substituent groups thereof bonded to the α carbons of the α-amino acids.