PURPOSE: To improve the working rate of the device by providing a magnetic field generating means for generating divergent magnetic fields along the progressing direction of microwaves near a microwave introducing window.

CONSTITUTION: This base body treatment device is provided with a reaction chamber 106 internally isolated from the atm. and the microwave introducing window 101 provided on the wall surface of this reaction chamber 106 in order to introduce microwave energy into the chamber. The device is also provided with a reactive gas supplying means (gaseous raw material introducing pipe) 104 for supplying reactive gases into the reaction chamber 106 and the microwave generating means for generating the microwaves to be introduced into the reaction chamber 106 via the microwave introducing window 101 to treat the base body 108 held in the reaction chamber 106. A magnet coil 102 as the magnetic field generating means to generate the divergent magnetic fields along the progressing direction of the microwaves near a microwave introducing window 101 is provided. The breakdown of the hermeticity of the reaction chamber is prevented and the safety of the device is improved.