Variable length coding method and variable length decoding method

A decoding apparatus which performs arithmetic decoding on a bit stream which is obtained by arithmetic coding, on a block basis, coefficients of a two-dimensional array of frequency components in a predetermined scanning order starting at a high frequency component toward a low frequency component, the coefficients being generated by frequency transformation performed on picture data of a block which has a predetermined size of pixels, the decoding apparatus comprising:

• an arithmetic decoding unit operable to perform arithmetic decoding on the bit stream to obtain Level values, on a block basis, according to a predetermined scanning order starting at a high frequency component toward a low frequency component by using a plurality of probability tables, the Level values each indicating a value of a non-zero coefficient, the value of which is non-zero;
• a table switching unit operable to switch a probability table to a new probability table based on a result of a comparison between an absolute value of a target Level value to be decoded and a predetermined threshold value;
• and
• a coefficient arranging unit operable to coefficient arrange, on a block basis, the decoded Level values into the two-dimensional array of frequency components;
• wherein the table switching unit performs the switching between a plurality of probability tables in one direction such that each probability table, which has been used before said new probability table, is not used after switching to said new probability table.