An apparatus for constructing a variable length code includes a unit for producing a unique word consisting of continuous N "0" bits, a prefix processing unit for producing a codeword including at least one "1" bit, the prefix of the codeword having continuous "0" bits with a length equal to or shorter than s, and a suffix processing unit for modifying a bit pattern of the produced codeword from the prefix processing unit so that the suffix of the codeword has continuous "0" bits with a bit length equal to or shorter than t, that a bit length of continuous "0" bits in the codeword is shorter than N, and that s+t