A tablet cassette comprising: a cassette body for storing tablets; and a rotor that is disposed rotatably in a bottom of a tablet container of the cassette body, the rotor having an outer peripheral surface on which a plurality of tablet guide grooves extending in a rotor rotation axial direction are formed, the rotor comprising: a plurality of movable pieces that are each disposed movably in a radial direction of the rotor in each of the plurality of tablet guide grooves and form surfaces in the radial direction of the rotor in the tablet guide grooves; a movable piece moving mechanism arranged to move the movable pieces in the radial direction of the rotor, the movable pieces moving mechanism being arranged to move the movable pieces in each of the plurality of tablet guide grooves in the radial direction of the rotor so as to adjust the groove depth of the plurality of tablet guide grooves, wherein the movable piece moving mechanism comprises: a rotor core member having a plurality of guide grooves for guiding the plurality of movable pieces in the radial direction of the rotor; and a movable piece driving plate that is disposed rotatably relative to the rotor core member and has a plurality of guide holes with which the plurality of movable pieces are engaged; and a rotation mechanism for rotating the movable piece driving plate. a cassette body for storing tablets; and a rotor that is disposed rotatably in a bottom of a tablet container of the cassette body, the rotor having an outer peripheral surface on which a plurality of tablet guide grooves extending in a rotor rotation axial direction are formed, the rotor comprising: a plurality of movable pieces that are each disposed movably in a radial direction of the rotor in each of the plurality of tablet guide grooves and form surfaces in the radial direction of the rotor in the tablet guide grooves; a movable piece moving mechanism arranged to move the movable pieces in the radial direction of the rotor, the movable pieces moving mechanism being arranged to move the movable pieces in each of the plurality of tablet guide grooves in the radial direction of the rotor so as to adjust the groove depth of the plurality of tablet guide grooves, a plurality of movable pieces that are each disposed movably in a radial direction of the rotor in each of the plurality of tablet guide grooves and form surfaces in the radial direction of the rotor in the tablet guide grooves; a movable piece moving mechanism arranged to move the movable pieces in the radial direction of the rotor, the movable pieces moving mechanism being arranged to move the movable pieces in each of the plurality of tablet guide grooves in the radial direction of the rotor so as to adjust the groove depth of the plurality of tablet guide grooves, wherein the movable piece moving mechanism comprises: a rotor core member having a plurality of guide grooves for guiding the plurality of movable pieces in the radial direction of the rotor; and a movable piece driving plate that is disposed rotatably relative to the rotor core member and has a plurality of guide holes with which the plurality of movable pieces are engaged; and a rotation mechanism for rotating the movable piece driving plate. a rotor core member having a plurality of guide grooves for guiding the plurality of movable pieces in the radial direction of the rotor; and a movable piece driving plate that is disposed rotatably relative to the rotor core member and has a plurality of guide holes with which the plurality of movable pieces are engaged; and a rotation mechanism for rotating the movable piece driving plate.