According to one embodiment, a host controller includes a command generator and detector. The command generator generates a command having a retransmission flag in an argument, and transmits the generated command to a memory device. The detector detects timeout if a response from the memory device cannot be recognized within a defined time. When transmitting an initial command, the host controller clears the retransmission flag and transmits the command. If the detector detects timeout, the host controller sets the retransmission flag, and retransmits the same command as the initial command to the device. If a normal response corresponding to the initial command or retransmitted command is received, the host controller recognizes that the command is correctly executed.