A power transmission device comprising a first power transmitter (110A, 110B, 110C) and a second power transmitter (110A, 110B, 110C), wherein the first power transmitter includes a first primary side resonance coil (13A, 13B, 13C) configured to receive power from an AC power source, a first phase difference detection unit configured to detect a first phase difference between a phase of a first current flowing to the first primary side resonance coil and a phase of a first voltage supplied to the first primary side resonance coil, a first variable capacitance unit (132A, 132B, 132C) provided at the first primary side resonance coil, and a first control unit (14A, 14B, 14C) configured to adjust a first capacitance of the first variable capacitance unit such that a resonance frequency is attained, based on a variation degree of the first phase difference with respect to a variation of the first capacitance when the first capacitance is varied, and wherein the second power transmitter includes a phase adjustment unit (240A, 240B) connected to the AC power source, a second primary side resonance coil (13A, 13B, 13C) configured to receive power from the AC power source via the phase adjustment unit, the second primary side resonance coil being arranged beside the first primary side resonance coil, a second phase difference detection unit configured to detect a second phase difference between a phase of a second current flowing to the second primary side resonance coil and a phase of a second voltage supplied to the second primary side resonance coil, a second variable capacitance unit (132A, 132B, 132C) provided at the second primary side resonance coil, and a second control unit (14A, 14B, 14C) configured to adjust a second capacitance of the second variable capacitance unit such that a resonance frequency is attained, based on a variation degree of the second phase difference to a variation of the second capacitance when the second capacitance is varied, and wherein the first control unit is configured to adjust the resonance frequency of the first power transmitter in a state where the second power transmitter is off, the second control unit is configured to adjust the resonance frequency of the second power transmitter in a state where the first power transmitter is off, the first control unit (14A, 14B, 14C) and the second control unit (14A, 14B, 14C) are respectively further configured to control on/off of the first power transmitter (110A, 110B, 110C) and the second power transmitter (110A, 110B, 110C), the first control unit is further configured to cause the second control unit to turn off the second power transmitter when the first control unit adjusts the resonance frequency of the first power transmitter, and the second control unit is further configured to cause the first control unit to turn off the first power transmitter when the second control unit adjusts the resonance frequency of the second power transmitter. a first primary side resonance coil (13A, 13B, 13C) configured to receive power from an AC power source, a first phase difference detection unit configured to detect a first phase difference between a phase of a first current flowing to the first primary side resonance coil and a phase of a first voltage supplied to the first primary side resonance coil, a first variable capacitance unit (132A, 132B, 132C) provided at the first primary side resonance coil, and a first control unit (14A, 14B, 14C) configured to adjust a first capacitance of the first variable capacitance unit such that a resonance frequency is attained, based on a variation degree of the first phase difference with respect to a variation of the first capacitance when the first capacitance is varied, and wherein a phase adjustment unit (240A, 240B) connected to the AC power source, a second primary side resonance coil (13A, 13B, 13C) configured to receive power from the AC power source via the phase adjustment unit, the second primary side resonance coil being arranged beside the first primary side resonance coil, a second phase difference detection unit configured to detect a second phase difference between a phase of a second current flowing to the second primary side resonance coil and a phase of a second voltage supplied to the second primary side resonance coil, a second variable capacitance unit (132A, 132B, 132C) provided at the second primary side resonance coil, and a second control unit (14A, 14B, 14C) configured to adjust a second capacitance of the second variable capacitance unit such that a resonance frequency is attained, based on a variation degree of the second phase difference to a variation of the second capacitance when the second capacitance is varied, and wherein the first control unit is further configured to cause the second control unit to turn off the second power transmitter when the first control unit adjusts the resonance frequency of the first power transmitter, and the second control unit is further configured to cause the first control unit to turn off the first power transmitter when the second control unit adjusts the resonance frequency of the second power transmitter.