A treatment system includes a treatment instrument that has a pair of freely openable/closable holding sections for applying thermal energy generated by a heat generation section to a living tissue LT held between the holding sections, a signal output section that supplies an alternating current drive signal to the heat generation section, a setting section that sets a target temperature of the heat generation section, a signal detection section that detects a current and a voltage of the drive signal, a control section that controls a temperature of the heat generation section by adjusting power of the drive signal, a signal extraction section that extracts a direct current component from the drive signal detected by the signal detection section and a fault detection section that detects a precursory phenomenon of a fault of the heat generation section based on the extracted signal extracted by the signal extraction section.