A bidirectional DC/DC converter, comprising: a first bridge circuit connected to a first direct current voltage supply and formed of a plurality of semiconductor switch elements (Q1-Q4); a second bridge circuit connected to a second direct current voltage supply and formed of a plurality of semiconductor switch elements (Q5-Q8); an isolating transformer that isolates the first bridge circuit and second bridge circuit; and a series resonant circuit connected between the alternating current side of the first bridge circuit and the isolating transformer, wherein power can be reciprocally supplied between the first direct current voltage supply and second direct current voltage supply by causing the first bridge circuit or second bridge circuit to carry out a switching operation, the bidirectional DC/DC converter further comprising: a first detector circuit that detects at least one of the voltage value or current value of the first direct current voltage supply; a second detector circuit that detects at least one of the voltage value or current value of the second direct current voltage supply; a second control circuit that controls the second bridge circuit based on a value detected by the first detector circuit; and a first control circuit that controls the first bridge circuit based on a value detected by the second detector circuit, wherein the first control circuit carries out pulse frequency modulation control of the first bridge circuit at a frequency equal to or lower than the resonance frequency of the series resonant circuit based on a control amount determined in accordance with a value detected by the second detector circuit when power is supplied from the first direct current voltage supply to the second direct current voltage supply, and the second control circuit carries out fixed frequency control of the second bridge circuit based on a control amount determined in accordance with a value detected by the first detector circuit when power is supplied from the second direct current voltage supply to the first direct current voltage supply. a first bridge circuit connected to a first direct current voltage supply and formed of a plurality of semiconductor switch elements (Q1-Q4); a second bridge circuit connected to a second direct current voltage supply and formed of a plurality of semiconductor switch elements (Q5-Q8); an isolating transformer that isolates the first bridge circuit and second bridge circuit; and a series resonant circuit connected between the alternating current side of the first bridge circuit and the isolating transformer, wherein power can be reciprocally supplied between the first direct current voltage supply and second direct current voltage supply by causing the first bridge circuit or second bridge circuit to carry out a switching operation, the bidirectional DC/DC converter further comprising: a first detector circuit that detects at least one of the voltage value or current value of the first direct current voltage supply; a second detector circuit that detects at least one of the voltage value or current value of the second direct current voltage supply; a second control circuit that controls the second bridge circuit based on a value detected by the first detector circuit; and a first control circuit that controls the first bridge circuit based on a value detected by the second detector circuit, wherein the first control circuit carries out pulse frequency modulation control of the first bridge circuit at a frequency equal to or lower than the resonance frequency of the series resonant circuit based on a control amount determined in accordance with a value detected by the second detector circuit when power is supplied from the first direct current voltage supply to the second direct current voltage supply, and the second control circuit carries out fixed frequency control of the second bridge circuit based on a control amount determined in accordance with a value detected by the first detector circuit when power is supplied from the second direct current voltage supply to the first direct current voltage supply. a first detector circuit that detects at least one of the voltage value or current value of the first direct current voltage supply; a second detector circuit that detects at least one of the voltage value or current value of the second direct current voltage supply; a second control circuit that controls the second bridge circuit based on a value detected by the first detector circuit; and a first control circuit that controls the first bridge circuit based on a value detected by the second detector circuit, wherein the first control circuit carries out pulse frequency modulation control of the first bridge circuit at a frequency equal to or lower than the resonance frequency of the series resonant circuit based on a control amount determined in accordance with a value detected by the second detector circuit when power is supplied from the first direct current voltage supply to the second direct current voltage supply, and the second control circuit carries out fixed frequency control of the second bridge circuit based on a control amount determined in accordance with a value detected by the first detector circuit when power is supplied from the second direct current voltage supply to the first direct current voltage supply.