To provide an operation method for performing continuous operation using a relatively small-scale backup equipment when the supply of power from the outside is stopped by power failure, or the like, and shortening a restarting time, in a method for distilling and separating a mixture having a separation factor at near to 1.

The distillatory apparatus is equipped with column stills 1, 2, 3 for concentrating a high boiling point component in a raw material, condensers 5, 7, 9 provided to the column stills 1, 2, 3, a heating medium circulating route for supplying a heating medium to the condensers 5, 7, 9 and a backup power supply source capable of supplying power to the heating medium circulating route at a time of power failure. Backup operation for continuing the operation of the distillatory apparatus using the backup power supply source at the time of power failure is performed and the supply amount of the raw material to the distillatory apparatus and the taking-out amount of a product from the distillatory apparatus are made smaller than those at a time of rated operation in the backup operation.