According to one embodiment, an information processor comprises a flush memory which stores a main program for executing information processing by using time data acquired through the clock count operation and a sub-program for upgrading a version of the main program of the information processing, a storage memory which stores the time data, and an arithmetic processing unit which executes the main program in starting the processor and executes the sub-program in upgrading the version, wherein the arithmetic processing unit executes the sub-program so as to continue the clock count operation even during execution of the version upgrading, and when the upgrading has completed, restarts the main program so as to restart the clock count operation by using the time data stored in the storage upon an execution start caused by restarting the main program.