An endoscope system 1 includes: a flexible endoscope 10 having a flexible insertion section 11, an operation section 12, and a flexible channel 14 that passes through the insertion section 11 a treatment tool 20 with a treatment unit 22 passing through the channel 14 and projecting from an opening 14B of a distal end portion a return electrode 40 and a power supply 30 for outputting high-frequency power, wherein the endoscope 10 has a power transmission unit 19 including a transmission electrode 18 for generating an alternating electric field to be applied to the channel by the high-frequency power input from the power supply 30, and the treatment tool 20 outputs, to the treatment unit 22, power received by a power reception unit 29 including a reception electrode 28 capacitively coupled to the transmission electrode 18.
