Abstract: An X-ray computer tomography apparatus equipped with an X-ray scanner for converting X-rays emitted from an X-ray source to a fan beam by a collimator, irradiating the fan beam to an object and detecting the X-rays passing through the object of a multi-channel X-ray detector includes a memory for storing data of a change quantity of a fan beam position with respect to a tilt angle of the X-ray scanner, a device for setting the X-ray scanner to a predetermined tilt angle, a control unit for controlling the position of the X-ray source so that the fan beam position becomes a reference position, on the basis of the change quantity of the fan beam position corresponding to the predetermined tilt angle read out from the memory and set, and a unit for executing X-ray tomography measurement or imaging of the object under the state where the fan beam position is controlled to the reference position.