1. An apparatus for decoding by using interpolation, the apparatus comprising: a decoder configured to decode an inputted bitstream; a data acquisition unit configured to acquire interpolation frame data, one or more reference frames, a macroblock type and one or more motion vector values from the decoder; and an interpolation processor configured to compute ratio data of an interpolation-target frame by using the interpolation frame data, and interpolating the interpolation-target frame by using the ratio data, pixel data of the one or more reference frames or the motion vector value according to the macroblock type, wherein the interpolation processor sets a same location of a pixel of a back reference frame as a location of an interpolation-target pixel of the interpolation-target frame if the macroblock type is a skipping macroblock (SKIP MB) or an INTRA macroblock (INTRA MB), wherein, if the macroblock type is the skipping macroblock (SKIP MB), the interpolation processor computes a pixel value of the interpolation-target pixel by multiplying one or more pixel data of the back reference frame and a front reference frame with the ratio data, and wherein, if the macroblock type is the INTRA macroblock (INTRA MB), the interpolation processor computes the pixel value of the interpolation-target pixel by using one or more pixel data of a reference frame between the front reference frame and the back reference frame adjacent to the interpolation-target frame, and wherein the ratio data is a ratio between a number of one or more interpolation-target frames and a number according to an order of an interpolation-target frame that is interpolated at a present time among the interpolation-target frames.