1. A charged particle beam irradiation system comprising: an accelerator for accelerating a charged particle beam to be extracted; an energy adjusting device through which the charged particle beam extracted from said accelerator passes; and a beam irradiation device for irradiating the charged particle beam having passed through said energy adjusting device to an irradiation target, wherein said energy adjusting device is rotatable and has different axial thicknesses in a rotating direction thereof; and said charged particle beam irradiation system further comprises a control unit for controlling starting and stopping of extraction of the charged particle beam from said accelerator in accordance with a rotational angle of said energy adjusting device and a dose of the charged particle beam having passed through said energy adjusting device.