The present invention provides a method and an apparatus for decoding videos, and also provides a method of updating a parameter used in entropy encoding and decoding of a transformation coefficient level. A syntax element indicating a transformation coefficient level is binarized by using a parameter. The parameter is renewed or maintained based on a result of comparing a size of a previous transformation coefficient with a predetermined critical value obtained based on a previous parameter used in de-binarization of a previous transformation coefficient level syntax element. The predetermined critical value is set to have a value proportional to the previous parameter, and when the previous parameter is renewed, the renewed parameter has a value that gradually increases compared to the previous parameter.