A controller may include a first processor suitable for sequentially storing commands provided from a host into one of first and second mailboxes of a memory according to types of the commands; and a second processor suitable for serving the commands stored in the first and second mailboxes, wherein, when provided from the host is a first command corresponding to the same logical address as a second command stored in the second mailbox, the first and second commands being of different types, the first processor stores the first command into the first mailbox and stores into the memory a priority information representing the second command having a higher processing priority to the first command, and wherein the second processor serves the commands stored in the first mailbox and the second mailbox by referring to the priority information.