An X-ray CT apparatus sets at least an imaging-subject area to be imaged, and a heart imaging area included in the imaging-subject area and determined based on a position and size of a heart on a subject P. The mount member has a supporting member whose one end is fixed to the power plant. The characteristics of the interlayer are chosen to form the roll with minimal lateral offset. The WSR apparatus of the present invention may be further equipped with servo-control and spectral power-management capabilities, thereby maintaining the coupling efficiencies of the spectral channels into the output ports at desired values. Slaving of hardware devices to the master hardware device can also be accomplished by finding a correlation between the clock times in memory and the reference clock.