PURPOSE: To obtain a subtraction picture with high picture quality by obtaining a smoothed picture data representing a smoothed picture from which a low spatial frequency component of a radiant ray picture is extracted or emphasized and applying subtraction processing while revising a parameter in response to the smoothed picture data corresponding to each picture element.

CONSTITUTION: Subtraction processing is applied to the entire picture while revising a parameter of subtraction processing for each part of the picture in response to the picture data. The picture data being a basis of the parameter revision obtains an average picture of plural radiant pictures based on the plural picture data representing each of the plural radiant ray picture and the parameter is revised in response to the picture data. Thus, noise component is reduced from the averaged picture more than that of the plural radiant ray picture. Thus, the subtraction picture with high picture quality is obtained.