An automatic analysis device comprising a reagent container containing a freeze-dried reagent, a reagent disk for holding the reagent container, a dispensing mechanism for dispensing a solvent into the reagent container, an inversion mixing mechanism for subjecting the reagent container to inversion mixing, and a control unit for controlling the dispensing mechanism and the inversion mixing mechanism, the inversion mixing mechanism having a rotating mechanism for rotating the reagent container, and a tilting mechanism for tilting a rotating shaft of the reagent container, the reagent container having a lid that can be pierced, the lid having a tubular mechanism that has an opening formed at a tip end and extends inside the reagent container, the control unit is configured to: after the reagent container containing the freeze-dried reagent is placed on the reagent disk, pierce the lid by the dispensing mechanism to form the opening, dispense a prescribed amount of solvent into the reagent container and control dispensing conditions of the dispensing mechanism so that the position of the opening formed at the tip end of the tubular mechanism is above the liquid surface of the solvent contained in the reagent container regardless of whether the reagent container is held upright, upside-down, or sideways by the inversion mixing mechanism, and then, after the reagent container having the solvent dispensed therein is transferred from the reagent disk to the inversion mixing mechanism, perform inversion mixing by tilting the rotation shaft of said tilting mechanism while rotating the reagent container placed in the inversion mixing mechanism. a reagent container containing a freeze-dried reagent, a reagent disk for holding the reagent container, a dispensing mechanism for dispensing a solvent into the reagent container, an inversion mixing mechanism for subjecting the reagent container to inversion mixing, and a control unit for controlling the dispensing mechanism and the inversion mixing mechanism, the inversion mixing mechanism having a rotating mechanism for rotating the reagent container, and a tilting mechanism for tilting a rotating shaft of the reagent container, a rotating mechanism for rotating the reagent container, and a tilting mechanism for tilting a rotating shaft of the reagent container, the reagent container having a lid that can be pierced, the lid having a tubular mechanism that has an opening formed at a tip end and extends inside the reagent container, the control unit is configured to: after the reagent container containing the freeze-dried reagent is placed on the reagent disk, pierce the lid by the dispensing mechanism to form the opening, dispense a prescribed amount of solvent into the reagent container and control dispensing conditions of the dispensing mechanism so that the position of the opening formed at the tip end of the tubular mechanism is above the liquid surface of the solvent contained in the reagent container regardless of whether the reagent container is held upright, upside-down, or sideways by the inversion mixing mechanism, and then, after the reagent container having the solvent dispensed therein is transferred from the reagent disk to the inversion mixing mechanism, perform inversion mixing by tilting the rotation shaft of said tilting mechanism while rotating the reagent container placed in the inversion mixing mechanism. after the reagent container containing the freeze-dried reagent is placed on the reagent disk, pierce the lid by the dispensing mechanism to form the opening, dispense a prescribed amount of solvent into the reagent container and control dispensing conditions of the dispensing mechanism so that the position of the opening formed at the tip end of the tubular mechanism is above the liquid surface of the solvent contained in the reagent container regardless of whether the reagent container is held upright, upside-down, or sideways by the inversion mixing mechanism, and then, after the reagent container having the solvent dispensed therein is transferred from the reagent disk to the inversion mixing mechanism, perform inversion mixing by tilting the rotation shaft of said tilting mechanism while rotating the reagent container placed in the inversion mixing mechanism.