A spring unit includes a composite spring and a metal wire. The composite spring is formed of resin, has a single beam structure, and includes a curved part between its end parts. The metal spring is formed of a metal wire, and includes a curved part between its end parts. The end parts of the composite spring are fixed to the corresponding end parts of the metal spring, so that the composite spring and the metal spring are fixed to be positioned in the same plane. The composite spring and the metal spring engage with each other in an engagement part formed in at least one position between the curved parts and the end parts. The composite spring and the metal spring are separated in a part other than the end parts and the engagement part.