In a charged particle beam exposure apparatus in which a charged particle beam is projected onto a member to be exposed to thereby form a pattern thereon, there are provided a plurality of electrodes disposed around an optical axis of the charged particle beam, a first unit for introducing a gas containing oxygen as a main component into an inside of the charged particle beam exposure apparatus including the plurality of electrodes and for holding the inside of the apparatus at a degree of vacuum between 0.1 Torr and 4 Torr, and a second unit for selectively applying either a high-frequency signal having a frequency between 100 kHz and 800 kHz or a reference signal to each of the plurality of electrodes. A plasma radical state of the gas is generated in the inside of the apparatus so that a deposition present in the apparatus can be eliminated.