Discrete cosine transform/inverse discrete cosine transform method and device are provided. The discrete cosine transform/inverse discrete cosine transform method includes: generating a table index for only an input value other than 0 (zero) out of input values of coordinates in an input block; reading one or more partial values corresponding to the table index out of a plurality of table information pieces which are generated and stored in advance so as to include partial values corresponding to a multiplication of a weight value and an index; and adding the read partial value and calculating the resultant value of each coordinate in an output block. Accordingly, it is possible to perform a fast DCT/IDCT operation and to reduce the energy consumption for the transform.