A system for calculating axial deformation of a turbine rotor, comprising: an input part that sets measurement points of a rotor disk that constitutes the turbine rotor; a deflection amount detection part that derives radial displacement amounts of the turbine rotor for at least four or more measurement points along an outer surface in a circumferential direction of the turbine rotor based on measured values measured by a displacement gage; a storage part that stores the radial displacement amounts derived by the deflection amount detection part and measured angles at the measurement points; and a calculation part that calculates misalignment data of a most probable circle of the turbine rotor based on data stored in the storage part, wherein the calculation part includes: a misalignment calculation part that calls up all the measurement points stored in the storage part, selects three arbitrary points to calculate a calculated circle from the radial displacement amounts and the measured angles, calculates calculated circle values for the measurement points from the calculated circle, calculates differences between the calculated circle values and the radial displacement amounts as error amounts at the measurement points, sums the error amounts to derive a total error amount value, repeats calculation for combinations of three measurement points among all the measurement points to calculate each total error amount value, selects a minimum calculated circle among obtained total error amount values for all combinations as a most probable circle, and calculates deviation between the center of the most probable circle and the center of rotation of the turbine rotor as the misalignment data of the most probable circle; a misalignment determination part that calculates a maximum misalignment amount with reference to the misalignment data of the most probable circle for all the rotor disks to determine whether the maximum misalignment amount is within a reference value or not; and an axial deformation distribution calculation part that calculates the distribution of axial deformation from the misalignment data of the most probable circle. an input part that sets measurement points of a rotor disk that constitutes the turbine rotor; a deflection amount detection part that derives radial displacement amounts of the turbine rotor for at least four or more measurement points along an outer surface in a circumferential direction of the turbine rotor based on measured values measured by a displacement gage; a storage part that stores the radial displacement amounts derived by the deflection amount detection part and measured angles at the measurement points; and a calculation part that calculates misalignment data of a most probable circle of the turbine rotor based on data stored in the storage part, wherein the calculation part includes: a misalignment calculation part that calls up all the measurement points stored in the storage part, selects three arbitrary points to calculate a calculated circle from the radial displacement amounts and the measured angles, calculates calculated circle values for the measurement points from the calculated circle, calculates differences between the calculated circle values and the radial displacement amounts as error amounts at the measurement points, sums the error amounts to derive a total error amount value, repeats calculation for combinations of three measurement points among all the measurement points to calculate each total error amount value, selects a minimum calculated circle among obtained total error amount values for all combinations as a most probable circle, and calculates deviation between the center of the most probable circle and the center of rotation of the turbine rotor as the misalignment data of the most probable circle; a misalignment determination part that calculates a maximum misalignment amount with reference to the misalignment data of the most probable circle for all the rotor disks to determine whether the maximum misalignment amount is within a reference value or not; and an axial deformation distribution calculation part that calculates the distribution of axial deformation from the misalignment data of the most probable circle. a misalignment calculation part that calls up all the measurement points stored in the storage part, selects three arbitrary points to calculate a calculated circle from the radial displacement amounts and the measured angles, calculates calculated circle values for the measurement points from the calculated circle, calculates differences between the calculated circle values and the radial displacement amounts as error amounts at the measurement points, sums the error amounts to derive a total error amount value, repeats calculation for combinations of three measurement points among all the measurement points to calculate each total error amount value, selects a minimum calculated circle among obtained total error amount values for all combinations as a most probable circle, and calculates deviation between the center of the most probable circle and the center of rotation of the turbine rotor as the misalignment data of the most probable circle; a misalignment determination part that calculates a maximum misalignment amount with reference to the misalignment data of the most probable circle for all the rotor disks to determine whether the maximum misalignment amount is within a reference value or not; and an axial deformation distribution calculation part that calculates the distribution of axial deformation from the misalignment data of the most probable circle.