An adhesive composition which comprises a resin component comprising a compound (A) obtained by replacing all or part of the oxirane rings of an epoxy compound with thiirane rings or comprising the compound (A) and a compound (B) having oxirane rings in the molecule but containing no thiirane rings and which has a high adhesion strength, rapid curability, etc.; a sealing resin composition excellent in adhesion and tensile strength; a resin composition for coating materials which has a satisfactory pot life and is excellent in curability, etc.; a resin composition for electrical use which comes to have electrical insulating properties in a short time, has flame retardancy, and is excellent in curability and adhesion to metals; a resin composition satisfactory in rapid curability and high-temperature storage stability; a resin composition which contains a specific phosphorous ester and is excellent in adhesion strength, low-temperature curability, etc.; a one-pack quick-curing resin composition which contains a specific ketimine and is excellent in low-temperature curability and storage stability; and a resin composition containing a reactive diluent with which viscosity reduction can be attained without causing the thiirane-containing resin to crystallize and thus make the composition milk-white.