An endoscope system 1 includes: an endoscope 10 having a flexible channel 14 that passes through an insertion section 11 a treatment tool 20 inserted from an insertion opening 14A of an operation section 12 of the endoscope 10 and passing through the channel 14 and a power supply 30 for outputting high-frequency power, wherein the endoscope 10 has a power transmission unit 19 including a first transmission electrode 18A and a second transmission electrode 18B to generate an alternating electric field applied to the channel 14 with the high-frequency power, and the treatment tool 20 has a power reception unit 29 including a first reception electrode 28A capacitively coupled to the first transmission electrode 18A and a second reception electrode 28B capacitively coupled to the second transmission electrode 18B to receive the alternating electric field so as to form, together with the power transmission unit 19, a resonance circuit having a resonant frequency identical to the frequency of high-frequency power.
