According to one embodiment, a command generator sequentially and speculatively issues channel-by-channel access commands to a memory interface in a predetermined access process. A purger returns a series of unexecuted already-issued access commands using a purge response if an error occurs in any of memory accesses via a plurality of channels. A command progress manager updates command progress information such that the command progress on each of the plurality of channels returns to a position specified in an oldest access command of a series of the returned access commands issued to the channel. The command generator issues the channel-by-channel access commands including the oldest access command to the memory interface based on the updated command progress information.