A bit rate converter for converting a first encoded animation image data to a second animation image data, having a different bit rate. The converter stores an assessment value indicating the importance level within each reproduction time interval with respect to the first animation image data. Second animation image data is generated by arithmetically determining the bit rate of the second animation image data on the basis of the bit rate information on the first animation image data and the assessment value indicating the importance level within a preselected time interval with respect to the first animation image data. Accordingly, a larger amount of code is preferentially allocated to the time interval having an assessment value of higher importance level.