Disclosed is an X-ray exposure apparatus having a low attenuation chamber (5) supplied with a gas absorbing little X-rays, the low attenuation chamber being interposed between an X-ray source (1) and a mask (9) so that X-rays (2) transmitted through the low attenuation chamber are irradiated on the mask so as to transfer a mask pattern onto a resist on a wafer (11), the apparatus comprising detecting means (13) for detecting the gas or components mixed in the gas in the low attenuation chamber, control means (14, 15, 16) for controlling a quantity of supply of the gas into the low attenuation chamber in accordance with an output signal of the detecting means, and/or adjusting means (21, 3) for adjusting a quantity of exposure of said X-rays irradiated on the mask in accordance with an output signal of the detecting means.