To provide a CT scanner with moving gantry which can easily retract a gantry during a power failure.

The gantry 7 includes a driving wheel 33 driven through a speed reducing machine whose reduction gear ratio is large, an auxiliary wheel 37 which is provided in the vicinity of the driving wheel 33 and can freely rotate, and a driving wheel lifting mechanism 50 for lifting the driving wheel 33 from a rail 5 and allowing the auxiliary wheel 37 to abutt on the rail 5.