A method maximizes efficiency of an end point memory in a USB device which conducts data communication with an external host. The method includes: assigning the memory to an end point at the point of time when the memory starts to be actually used; and returning the memory, which was assigned to the end point, at the point of time when the actual use of the memory is ended. When the end point is a reception end point, the point of time when the actual use starts is a point of time when the USB device receives an OUT token from the host, and the point of time when the actual use is ended is a point of time when the USB device confirms that data received from the host have no errors.