A calculation method for a sublimation interface temperature, a bottom part temperature, and a sublimation rate of a material to be dried in a freeze-drying device, comprising: a drying chamber into which the to-be-dried material is introduced; a cold trap for condensing and trapping water vapor generated from the to-be-dried material introduced into the drying chamber; a main pipe (a) for providing communication between the drying chamber and the cold trap; a main valve for opening and closing the main pipe (a); vacuum adjustment means for adjusting the degree of vacuum in the drying chamber; vacuum detection means for detecting an absolute pressure in the drying chamber and an absolute pressure in the cold trap; and a control device for automatically controlling the operations of the drying chamber, of the cold trap, and of the vacuum adjustment means, wherein the main pipe (a) includes a damper-type opening adjustment device for adjusting an opening angle of the main pipe (a) as the vacuum adjustment means, the control device stores a calculation program and a relational expression which describes a relationship between a sublimation rate (Qm) under water load in a state where the main valve is fully open, an opening angle (θ) of the opening adjustment device, and a main pipe resistance R(θ); and the control device turns the opening adjustment device at least once in an opening direction during the primary drying period of the to-be-dried material introduced into the drying chamber to temporarily change the degree of vacuum (Pdc) in the drying chamber in the increasing direction, and calculates the average sublimation interface temperature, the bottom part temperature, and the sublimation rate of the to-be-dried material that prevail during the primary drying period in accordance with the relational expression and measured data about the opening angle (θ) of the opening adjustment device, the degree of vacuum (Pdc) in the drying chamber, and the degree of vacuum (Pdt) in the cold trap, which are obtained before and after an operation in an opening-direction of the opening adjustment device. a drying chamber into which the to-be-dried material is introduced; a cold trap for condensing and trapping water vapor generated from the to-be-dried material introduced into the drying chamber; a main pipe (a) for providing communication between the drying chamber and the cold trap; a main valve for opening and closing the main pipe (a); vacuum adjustment means for adjusting the degree of vacuum in the drying chamber; vacuum detection means for detecting an absolute pressure in the drying chamber and an absolute pressure in the cold trap; and a control device for automatically controlling the operations of the drying chamber, of the cold trap, and of the vacuum adjustment means, wherein the main pipe (a) includes a damper-type opening adjustment device for adjusting an opening angle of the main pipe (a) as the vacuum adjustment means, the control device stores a calculation program and a relational expression which describes a relationship between a sublimation rate (Qm) under water load in a state where the main valve is fully open, an opening angle (θ) of the opening adjustment device, and a main pipe resistance R(θ); and the control device turns the opening adjustment device at least once in an opening direction during the primary drying period of the to-be-dried material introduced into the drying chamber to temporarily change the degree of vacuum (Pdc) in the drying chamber in the increasing direction, and calculates the average sublimation interface temperature, the bottom part temperature, and the sublimation rate of the to-be-dried material that prevail during the primary drying period in accordance with the relational expression and measured data about the opening angle (θ) of the opening adjustment device, the degree of vacuum (Pdc) in the drying chamber, and the degree of vacuum (Pdt) in the cold trap, which are obtained before and after an operation in an opening-direction of the opening adjustment device.