A body thickness conversion unit converts a body thickness from a distance image imaged by a distance measurement camera to acquire the body thickness. A setting unit sets a gradation transformation function for use in gradation transformation processing to a radiographic image corresponding to the body thickness. A radiographic image acquisition unit acquires the radiographic image output from a radiation detector in radioscopy. A gradation transformation processing unit starts the gradation transformation processing with the gradation transformation function set by the setting unit.