A viscosity estimation device (1, 2) configured to estimate a viscosity of a substance stirred by a rotation of a rotating shaft rotationally driven by an induction motor, the viscosity estimation device comprising: a current detector detecting a drive current supplied to the induction motor; a rotation detector (20, 20A) detecting rotation of the rotating shaft; and a calculator (30, 30A) obtaining a viscosity correlation value, which is a value having a correlation with a viscosity of the substance, using a detection result of the current detector and a detection result of the rotation detector (20, 20A), wherein the calculator (30, 30A) comprises: a slip ratio calculator obtaining a slip ratio of the rotating shaft using the detection result of the current detector and the detection result of the rotation detector (20, 20A); an effective value calculator obtaining an effective value of the drive current from the detection result of the current detector; a frequency calculator obtaining a frequency of the drive current from the detection result of the current detector; a viscosity correlation value calculator obtaining the viscosity correlation value using a calculation result of the slip ratio calculator, a calculation result of the effective value calculator, and a calculation result of the frequency calculator; and a viscosity correlation value viscosity calculator converting the viscosity correlation value obtained by the viscosity correlation value calculator into a viscosity value of the substance, the conversion being performed based on a variable which defines a scale factor of the viscosity correlation value and a variable which defines an offset of the viscosity correlation value, characterized in that the viscosity correlation value calculator is configured to obtain the viscosity correlation value by multiplying: a value obtained by dividing the frequency of the drive current by a rotation speed of the rotating shaft obtained by the detection result of the rotation detector (20, 20A); square of the effective value of the drive current; and the slip ratio of the rotating shaft. a current detector detecting a drive current supplied to the induction motor; a rotation detector (20, 20A) detecting rotation of the rotating shaft; and a calculator (30, 30A) obtaining a viscosity correlation value, which is a value having a correlation with a viscosity of the substance, using a detection result of the current detector and a detection result of the rotation detector (20, 20A), wherein the calculator (30, 30A) comprises: a slip ratio calculator obtaining a slip ratio of the rotating shaft using the detection result of the current detector and the detection result of the rotation detector (20, 20A); an effective value calculator obtaining an effective value of the drive current from the detection result of the current detector; a frequency calculator obtaining a frequency of the drive current from the detection result of the current detector; a viscosity correlation value calculator obtaining the viscosity correlation value using a calculation result of the slip ratio calculator, a calculation result of the effective value calculator, and a calculation result of the frequency calculator; and a viscosity correlation value viscosity calculator converting the viscosity correlation value obtained by the viscosity correlation value calculator into a viscosity value of the substance, the conversion being performed based on a variable which defines a scale factor of the viscosity correlation value and a variable which defines an offset of the viscosity correlation value, a slip ratio calculator obtaining a slip ratio of the rotating shaft using the detection result of the current detector and the detection result of the rotation detector (20, 20A); an effective value calculator obtaining an effective value of the drive current from the detection result of the current detector; a frequency calculator obtaining a frequency of the drive current from the detection result of the current detector; a viscosity correlation value calculator obtaining the viscosity correlation value using a calculation result of the slip ratio calculator, a calculation result of the effective value calculator, and a calculation result of the frequency calculator; and a viscosity correlation value viscosity calculator converting the viscosity correlation value obtained by the viscosity correlation value calculator into a viscosity value of the substance, the conversion being performed based on a variable which defines a scale factor of the viscosity correlation value and a variable which defines an offset of the viscosity correlation value, characterized in that the viscosity correlation value calculator is configured to obtain the viscosity correlation value by multiplying: a value obtained by dividing the frequency of the drive current by a rotation speed of the rotating shaft obtained by the detection result of the rotation detector (20, 20A); square of the effective value of the drive current; and the slip ratio of the rotating shaft.