An X-ray CT apparatus has an X-ray source, an X-ray detector, a temperature sensor, a data acquisition unit and a controller. The X-ray source generates an X-ray. The X-ray detector detects the X-ray. The temperature sensor detects a temperature of the X-ray detector. The data acquisition unit acquires data from the X-ray detector. The controller controls a temperature of the X-ray detector through adjustment of a workload of the data acquisition unit during a non-scanning time.