An X-ray computed tomography apparatus includes a controller for shifting an X-ray focal spot position of an X-ray source, a plurality of first temporary holding devices respectively connected to X-ray detector elements to temporarily hold measured values of X-ray intensity transmitted through an object to be incident on the X-ray detector elements, a switch device for switching over connection between the X-ray detector elements and the first temporary holding devices, a controller for controlling switchover of the switch device, a transfer device for transferring the measured values from the first temporary holding devices to an interpolation calculating device, an interpolation calculating device for performing interpolation calculations on the projection data to generate projection data equivalent to projection data measured by using a measuring system virtually having twice as many X-ray detector elements as the arranged X-ray detector elements, a memory for holding parameters used for calculations in the interpolation calculating device, and an image reconstructor for reconstructing a tomographic image on the basis of the projection data generated by interpolation calculating device.