An internal paddle electrode includes: an electrode which is to be in contact with a living body to apply a voltage a cable which includes a voltage supply path that extends between a voltage supply source and the electrode a handle which includes: a first portion that supports the electrode and is hermetically sealed with the electrode and a second portion that is connected to the cable and is hermetically sealed with the cable and a gas passage through which a gas in the handle communicates with external air that is outside the handle.
