A relay state determination device that determines whether or not a relay has deteriorated, the relay including: a primary-side switch, an operation coil, and a shunt resistor that are connected in series to a primary-side power supply; a diode connected in parallel to a series connection of the operation coil and the shunt resistor in a direction in which current due to a counter electromotive force of the operation coil flows to the shunt resistor when the primary-side switch is turned off; and an armature that opens and closes at least a pair of secondary-side contacts in response to on and off of the primary-side switch, the armature being configured to be displaced relative to the operation coil by an electromagnetic force generated by the operation coil when the primary-side switch is turned on and to bring one of the secondary-side contacts into contact with an other of the secondary-side contacts while being deflected by a certain push-in amount, the relay state determination device comprising: a voltage value acquisition unit that measures every moment a detected voltage detected from two ends of the shunt resistor; characterized in that the relay state determination device further comprises: a voltage value difference calculation unit that calculates a voltage value difference between a first voltage value of when the detected voltage becomes minimum by the armature starting displacement after the primary-side switch is turned off and a second voltage value of when the secondary-side contacts are opened; and a state determination unit that determines that the relay has deteriorated when the voltage value difference falls below a predetermined threshold value. a primary-side switch, an operation coil, and a shunt resistor that are connected in series to a primary-side power supply; a diode connected in parallel to a series connection of the operation coil and the shunt resistor in a direction in which current due to a counter electromotive force of the operation coil flows to the shunt resistor when the primary-side switch is turned off; and an armature that opens and closes at least a pair of secondary-side contacts in response to on and off of the primary-side switch, the armature being configured to be displaced relative to the operation coil by an electromagnetic force generated by the operation coil when the primary-side switch is turned on and to bring one of the secondary-side contacts into contact with an other of the secondary-side contacts while being deflected by a certain push-in amount, the relay state determination device comprising: a voltage value acquisition unit that measures every moment a detected voltage detected from two ends of the shunt resistor; characterized in that the relay state determination device further comprises: a voltage value difference calculation unit that calculates a voltage value difference between a first voltage value of when the detected voltage becomes minimum by the armature starting displacement after the primary-side switch is turned off and a second voltage value of when the secondary-side contacts are opened; and a state determination unit that determines that the relay has deteriorated when the voltage value difference falls below a predetermined threshold value. a voltage value acquisition unit that measures every moment a detected voltage detected from two ends of the shunt resistor; characterized in that the relay state determination device further comprises: a voltage value difference calculation unit that calculates a voltage value difference between a first voltage value of when the detected voltage becomes minimum by the armature starting displacement after the primary-side switch is turned off and a second voltage value of when the secondary-side contacts are opened; and a state determination unit that determines that the relay has deteriorated when the voltage value difference falls below a predetermined threshold value. a voltage value difference calculation unit that calculates a voltage value difference between a first voltage value of when the detected voltage becomes minimum by the armature starting displacement after the primary-side switch is turned off and a second voltage value of when the secondary-side contacts are opened; and a state determination unit that determines that the relay has deteriorated when the voltage value difference falls below a predetermined threshold value.