To provide a compound having a new lactone skeleton which is useful as a constituent monomer for photoresist resins.

The α-unsaturated acyloxy-γ-butylolactone derivative is represented by formula (1) (wherein Ra is a hydrogen atom, a halogen atom, a 1-6C alkyl group or a 1-6C haloalkyl group; Rb is a hydrocarbon group (except for a hydrocarbon group having a tertiary carbon atom at bonding position with adjacent oxygen atom); R1 and R2 are same or different and they are each a hydrocarbon group and R1 and R2 may mutually be combined to form a ring together with an adjacent carbon atom; R3 and R4 are same or different and they are each hydrogen atom or a hydrocarbon group).