Multiple-energy operation with quasi-DC extension of flattops is developed at the HIMAC. This operation uses synchrotron operation-patterns having a stepwise flattop. With these patterns, the beam would be first accelerated to the maximum energy, and then successively decelerated to the lower energies. Having extended the flattops and extracted the beam during these flattops, heavy ions having various energies can be provided within a single synchrotron cycle. Since the extraction energy can be quickly changed by the accelerator itself, no energy degrader will be required to control a depth dosedistribution. Having applied this multiple-energy operation to our fast raster-scanning irradiation, we can considerably reduce the total irradiation time and obtain an excellent depth dose-distribution. The beam acceleration and extraction tests using this operation were made. Successful results of the tests proved the effectiveness of this multiple-energy operation.