A method of measuring a degree of degradation/alteration of a lubricating oil, the method comprising: measuring a dielectric constant or electrostatic capacitance of a lubricating oil at two or more different frequencies; and determining a degradation/alteration state of the lubricating oil based on values of the dielectric constants or the electrostatic capacitances, wherein the method further comprises: measuring a dielectric constant (ε 1) or an electrostatic capacitance (C 1) of the lubricating oil at a frequency H 1 and a dielectric constant (ε 2) or an electrostatic capacitance (C 2) of the lubricating oil at the frequency H 2; determining that the lubricating oil has been degraded/altered when a value of the dielectric constant (ε 1) or the electrostatic capacitance (C 1) or a value of the dielectric constant (ε 2) or the electrostatic capacitance (C 2) has reached a set value; and characterized in that the method further comprises the step of predicting a degradation/alteration mechanism of the lubricating oil based on a rate of a change in dielectric constant with respect to the frequency [(ε 1 -ε 2)/(H 2 -H 1)] or a rate of a change in electrostatic capacitance with respect to the frequency [(C 1 -C 2)/(H 2 -H 1)], wherein one frequency (H 1) of the two or more different frequencies is in a range of 1 to 100 Hz, and another frequency (H 2) is more than H 1 and in a range of 10,000 Hz or less. measuring a dielectric constant or electrostatic capacitance of a lubricating oil at two or more different frequencies; and determining a degradation/alteration state of the lubricating oil based on values of the dielectric constants or the electrostatic capacitances, wherein the method further comprises: measuring a dielectric constant (ε 1) or an electrostatic capacitance (C 1) of the lubricating oil at a frequency H 1 and a dielectric constant (ε 2) or an electrostatic capacitance (C 2) of the lubricating oil at the frequency H 2; determining that the lubricating oil has been degraded/altered when a value of the dielectric constant (ε 1) or the electrostatic capacitance (C 1) or a value of the dielectric constant (ε 2) or the electrostatic capacitance (C 2) has reached a set value; and characterized in that the method further comprises the step of predicting a degradation/alteration mechanism of the lubricating oil based on a rate of a change in dielectric constant with respect to the frequency [(ε 1 -ε 2)/(H 2 -H 1)] or a rate of a change in electrostatic capacitance with respect to the frequency [(C 1 -C 2)/(H 2 -H 1)], wherein one frequency (H 1) of the two or more different frequencies is in a range of 1 to 100 Hz, and another frequency (H 2) is more than H 1 and in a range of 10,000 Hz or less. measuring a dielectric constant (ε 1) or an electrostatic capacitance (C 1) of the lubricating oil at a frequency H 1 and a dielectric constant (ε 2) or an electrostatic capacitance (C 2) of the lubricating oil at the frequency H 2; determining that the lubricating oil has been degraded/altered when a value of the dielectric constant (ε 1) or the electrostatic capacitance (C 1) or a value of the dielectric constant (ε 2) or the electrostatic capacitance (C 2) has reached a set value; and characterized in that the method further comprises the step of predicting a degradation/alteration mechanism of the lubricating oil based on a rate of a change in dielectric constant with respect to the frequency [(ε 1 -ε 2)/(H 2 -H 1)] or a rate of a change in electrostatic capacitance with respect to the frequency [(C 1 -C 2)/(H 2 -H 1)], wherein one frequency (H 1) of the two or more different frequencies is in a range of 1 to 100 Hz, and another frequency (H 2) is more than H 1 and in a range of 10,000 Hz or less.