To provide a medical instrument with which a therapy can be performed, regardless of the original site of cancer.

The medical instruments 10, 20, 30 include: needle tubes 11, 31 which are formed of conductive cylindrical members to be connected to a positive or negative electrode, and have medicial solution injection holes on the side surfaces of the distal ends; needle bodies 12, 32 which are insertable from proximal end sides into the inner parts of the needle tubes 11, 31, formed of conductive needle shape members to be connected to the opposite electrodes of the needle tubes 11, 31, and provided with insulating parts 15, 33 on the outer peripheral surfaces in contact with the inner surfaces of the needle tubes 11, 31; and heat generation bodies 14, 34 with prescribed heat generation resistances, which are arranged so as to clog the openings at the distal ends of the needle tubes 11, 31 and also to come in contact with the distal ends of the needle bodies 12, 32. When the needle bodies 12, 32 are inserted from the proximal end sides into the inner parts of the needle tubes 11, 31 to thereby allow the distal ends of the needle bodies 12, 32 to come in contact with the heat generation bodies 14, 34, the needle bodies 12, 32 and the needle tubes 11, 31 are energized via the heat generation bodies 14, 34.