An accumulator mechanism suitable to be included in an on-load tap changer, and to perform a changing operation on a shutoff mechanism upon reception of drive force from an electric actuator mechanism, the accumulator mechanism comprising: a spring; a winding casing that abuts one end of the spring, and is slidable in a direction in which the spring is compressed; an accumulating casing that abuts an other end of the spring and is slidable in a direction in which the spring is elongated; a crank that abuts the accumulating casing, and rotates in a manner linked with sliding of the accumulating casing; a drive rod that is provided in a manner coaxial with the crank, and transmits rotational force to the shutoff mechanism; a catch (31A, 31B) that holds the accumulating casing and the crank until the winding casing compresses the spring; characterized by an eccentric cam that is provided outside an area where the spring, the winding casing, the accumulating casing, and the catch are retained, is linked with the winding casing from an exterior thereof through a swingable joint, and slides the winding casing through the swingable joint when rotated by the electric actuator mechanism; and a forcible loading mechanism that directly rotates the crank together with a rotating operation of the eccentric cam, wherein the forcible loading mechanism comprises: a gear having gear teeth provided on a circle coaxial with a rotation trajectory of the eccentric cam; and a slider that linearly moves in a rotation tangent-line direction of the crank upon rotation of the gear, and is linked with the crank. a spring; a winding casing that abuts one end of the spring, and is slidable in a direction in which the spring is compressed; an accumulating casing that abuts an other end of the spring and is slidable in a direction in which the spring is elongated; a crank that abuts the accumulating casing, and rotates in a manner linked with sliding of the accumulating casing; a drive rod that is provided in a manner coaxial with the crank, and transmits rotational force to the shutoff mechanism; a catch (31A, 31B) that holds the accumulating casing and the crank until the winding casing compresses the spring; characterized by an eccentric cam that is provided outside an area where the spring, the winding casing, the accumulating casing, and the catch are retained, is linked with the winding casing from an exterior thereof through a swingable joint, and slides the winding casing through the swingable joint when rotated by the electric actuator mechanism; and a forcible loading mechanism that directly rotates the crank together with a rotating operation of the eccentric cam, wherein the forcible loading mechanism comprises: a gear having gear teeth provided on a circle coaxial with a rotation trajectory of the eccentric cam; and a slider that linearly moves in a rotation tangent-line direction of the crank upon rotation of the gear, and is linked with the crank. a gear having gear teeth provided on a circle coaxial with a rotation trajectory of the eccentric cam; and a slider that linearly moves in a rotation tangent-line direction of the crank upon rotation of the gear, and is linked with the crank.