An X-ray imaging system has two types of electronic cassettes and one type of IP cassette. Upon entering a body portion to be imaged, an input and output controller retrieves from an imaging condition table of the IP cassette an imaging condition corresponding to the body portion as a reference imaging condition. An imaging condition calculator multiplies reference exposure time of the reference imaging condition by a sensitivity coefficient of each electronic cassette, to calculate an imaging condition to be applied in using each electronic cassette. An input and output controller displays the imaging conditions of the electronic cassettes and the IP cassette and choice buttons for choosing one of the electronic cassettes and the IP cassette in a list form on a monitor.