Provided is a differential precoding method for reducing inter-user interference and increasing the sum rate. The differential precoding method comprises initializing a precoding matrix with a first (Precoding Matrix Indicator (PMI) for a channel between a mobile station and a base station; and updating the precoding matrix with a second PMI for the channel and side information for adaptively updating the precoding matrix according to a change speed of a state of the channel, wherein the side information has a quantized scalar value.