A portable storage apparatus capable of freely changing a data bus width and a method of setting the data bus width of the apparatus are provided, where the portable storage apparatus has at least one command line and a plurality of data lines, and includes a non-volatile memory, a command packet decoder, and a control unit, such that the non-volatile memory stores data, the command packet decoder receives command packets through a command line and outputs command information by decoding the received command packets, the command packet decoder receives a data transmit command packet or a data request command packet and outputs a write command or a read command, address information, and data bus width information, the control unit performs a control operation in response to the command information and selects all or some of the plurality of data lines in response to the data bus width information and receives or transmits the data through the selected data line, and controls data writing or reading of the non-volatile memory in response to the write command or the read command and the address information, thereby not requiring the data bus width to be set in advance and enabling free adjustment of the data bus width, if necessary.