An X-ray distribution adjusting filter apparatus for supplying a desired X-ray intensity distribution or adjusting the X-ray distribution to a desired profile, the bowtie filter as the X-ray distribution adjusting filter apparatus has a fixed section having a base portion and inclined portions, first and second movable sections configured to be tiltable pivoting on a center point, and first and second deformable sections whose cavities defined by the fixed section, the movable sections and an expansible bellows is to be filled with fluid, wherein the inclined faces of the fixed section and the flat faces of the movable sections are caused to approach or move away from each other by the tilting of the movable sections pivoting on the center point to vary the quantity of the fluid in the cavities of the movable sections, and to vary the sectional shape of the X-ray absorbing portion of the bowtie filter.