RESISTANCE VALUE CALCULATION DEVICE

PROBLEM TO BE SOLVED: To grasp a decrease in a resistance value of an insulation resistance of a loading device during an operation of a power supply system.SOLUTION: A resistance value calculation device calculates resistance values of first and second insulation resistances of a loading device having the first insulation resistance between a positive line and an earth, and the second insulation resistance between a negative line and the earth. The resistance value calculation device has: a first potential difference measurement unit that measures a potential difference between both ends of a first ground resistance provided on a first ground line that connects the positive line and the earth; a second potential difference measurement unit that measures a potential difference between both ends of a second ground resistance provided on a second ground line that connects the negative line and the earth; a control unit that calculates resistance values of the first and second insulation resistances using a variable resistor provided on the first or second ground line, a resistance value before and after the variation of the variable resistor, potential difference measured by the first and second potential difference measurement units before and after the variation, and resistance values of the first and second ground resistances; and an output unit that outputs the calculated resistance values for notifying them to the outside.