A power conditioner that is configured to boost a direct current output from a first power supply being a first photovoltaic cell, a first photovoltaic module in which first photovoltaic cells are connected in series or parallel, or a first fuel cell, to convert the boosted direct current into an alternating current, and to output the alternating current onto a side of a system power supply, the power conditioner comprising: a first boost circuit that comprises a first switch (Tra) connected between output terminals of the first power supply, a first coil (L1a) or first transformer winding configured to boost a voltage from the first power supply by turning on and off the first switch (Tra), and a first backflow prevention circuit (Da) configured to rectify an output from the first coil (L1a) or the first transformer winding; a second boost circuit configured to boost a voltage at a second power supply being a second photovoltaic cell, a second photovoltaic module in which second photovoltaic cells are connected in series or parallel, or a second fuel cell; a connection unit configured to connect an output side of the first boost circuit and an output side of the second boost circuit in parallel with each other, a potential controller configured to perform control such that a potential at the first backflow prevention circuit (Da) on the side opposite to the first power supply is greater than or equal to a potential at the first backflow prevention circuit (Da) on the side of the first power supply during an off period of the first switch (Tra); an open-circuit voltage value acquisition unit configured to acquire a first open-circuit voltage value of the first power supply, when the first switch (Tra) is in the off period while the potential controller performs the control such that the voltage at the first backflow prevention circuit (Da) on the side opposite to the first power supply is greater than or equal to the voltage at the first backflow prevention circuit (Da) on the side of the first power supply; and a power supply abnormality determination unit configured to determine whether the first power supply has an abnormality based on comparison between the first open-circuit voltage value and a first reference voltage value that is previously fixed based on a characteristic of the first power supply, wherein the potential controller is adapted to perform the control such that the voltage at the connection unit is greater than or equal to the voltage on an input side of the first boost circuit by turning on and off a second switch (Trb) included in the second boost circuit when the open-circuit voltage value acquisition unit acquires the first open-circuit voltage value, so that the potential controller is adapted to perform the control such that the potential at the first backflow prevention circuit (Da) on the side opposite to the first power supply is greater than or equal to the potential at the first backflow prevention circuit (Da) on the side of the first power supply. a first boost circuit that comprises a first switch (Tra) connected between output terminals of the first power supply, a first coil (L1a) or first transformer winding configured to boost a voltage from the first power supply by turning on and off the first switch (Tra), and a first backflow prevention circuit (Da) configured to rectify an output from the first coil (L1a) or the first transformer winding; a second boost circuit configured to boost a voltage at a second power supply being a second photovoltaic cell, a second photovoltaic module in which second photovoltaic cells are connected in series or parallel, or a second fuel cell; a connection unit configured to connect an output side of the first boost circuit and an output side of the second boost circuit in parallel with each other, a potential controller configured to perform control such that a potential at the first backflow prevention circuit (Da) on the side opposite to the first power supply is greater than or equal to a potential at the first backflow prevention circuit (Da) on the side of the first power supply during an off period of the first switch (Tra); an open-circuit voltage value acquisition unit configured to acquire a first open-circuit voltage value of the first power supply, when the first switch (Tra) is in the off period while the potential controller performs the control such that the voltage at the first backflow prevention circuit (Da) on the side opposite to the first power supply is greater than or equal to the voltage at the first backflow prevention circuit (Da) on the side of the first power supply; and a power supply abnormality determination unit configured to determine whether the first power supply has an abnormality based on comparison between the first open-circuit voltage value and a first reference voltage value that is previously fixed based on a characteristic of the first power supply, wherein the potential controller is adapted to perform the control such that the voltage at the connection unit is greater than or equal to the voltage on an input side of the first boost circuit by turning on and off a second switch (Trb) included in the second boost circuit when the open-circuit voltage value acquisition unit acquires the first open-circuit voltage value, so that the potential controller is adapted to perform the control such that the potential at the first backflow prevention circuit (Da) on the side opposite to the first power supply is greater than or equal to the potential at the first backflow prevention circuit (Da) on the side of the first power supply.