1. An image decoding method comprising the steps of: receiving an encoded bitstream including information; and executing motion compensation by synthesizing a predicted image of a current frame using motion vector information included in the encoded bitstream and a reference image which is a previously decoded image; wherein the synthesizing a prediction image is performable using a positive rounding method and a negative rounding method for interpolating intensity values of pixels; wherein the interpolating intensity values of pixels is performed using a rounding method specified by the rounding method information; wherein the rounding method information is included in coded information of the currently decoded image; and wherein the rounding method information is included in a header section of the coded information of the currently decoded image; wherein the rounding method information specifies one of two values; wherein one of the two values specifies a positive rounding method, and another one of the two values specifies a negative rounding method; and wherein the rounding method information consists of one bit.