A trocar comprising: a housing; an insertion tube that is integral with the housing and is inserted into a subject; a power transmission coil that is disposed inside of the housing and generates AC magnetic field to be applied to an insertion hole into which a treatment tool is to be inserted; a radiator that transmits heat generated from the power transmission coil; and a heat insulator disposed on a side of the subject between the radiator and the subject, the heat insulator having lower thermal conductivity than the radiator.