an ignition chamber unit to be arranged on a main combustion chamber of an internal combustion engine has walls forming a separate ignition chamber having a first wall which separates the ignition chamber from the main combustion chamber and has at least one passage arranged in the first wall to connect the ignition chamber with the combustion chamber , a center electrode provided in the ignition chamber and forming together with the first wall a spark gap and also having a free end which extends into the ignition chamber , wherein the electrode is hollow near the free end and is formed as a heat pipe , and an insulator with an insulator shoe which extends into the ignition chamber and supports the center electrode so that the insulator together with the insulator shoe forms an insulating gap .