A charged particle beam generator, a charged particle irradiation system, a method for operating the charged particle beam generator and a method for operating the charged particle irradiation system, which allow a charged particle beam to be injected into a circular accelerator 200 at an arbitrary timing and can reduce an irradiation time and a time for a therapy, are provided while maintaining the lower limit of an operation cycle of a linear accelerator 111. An accelerator control device 210 controls an operation of a synchrotron 200 on the basis of a beam extraction request signal transmitted from a beam utilization system control device. A control device 210 generates a timing signal notifying the linear accelerator 111 of an injection timing of a next operation cycle of the synchrotron 200 after completion of an extraction process performed by the synchrotron 200, changes an operation timing of the linear accelerator 111 so that the operation timing of the linear accelerator 111 matches the injection timing.
