An Information compression-coding method of compression-coding an inputted bit string, wherein strings of pieces of dictionary information and indices corresponding to the strings of pieces of dictionary information are registered in a dictionary part, the dictionary information being composed of a predetermined plurality of bits, letting the inputted bit string be defined as a string of pieces of unit processing information composed of a predetermined plurality of bits, and letting information for determining whether each of bits in the string of the pieces of unit processing information is effective or not be defined as effective bits information, the information compression-coding method comprising: an input step inputting strings of samples including sample strings having a variable length; a unit processing information generating step for generating a sequence of bit groups to be subjected to encoding as unit processing information; an effective bits information generating step of generating effective bits information corresponding to the unit processing information; a search step of obtaining an index of one of the strings of pieces of dictionary information that provides a match, for effective bits of each piece of unit processing information, with a largest number of sequential pieces to be coded in the string of pieces of unit processing information, the effective bits being determined by the effective bits information corresponding to the each piece of unit processing information; and an output step of outputting the index obtained at the search step or a code representing the index; wherein: in the unit processing information generating step sample strings (s1, s2,...) having a variable length are converted into a definite-length character string to retain the correlation among or within samples, each character string being composed of one or more bit groups, wherein if the number of bits of a sample is not an integral multiple of a predetermined number of bits matching to the size of pieces of dictionary information registered in the dictionary part, so that residual bits are left at a MSB side or LSB side of the sample, respectively, dummy bits are added to the residual bits from the MSB side or LSB side, respectively, until the number of bits according to the predetermined number of bits of the bit group is reached, so that each sample becomes an integral multiple of the predetermined number of bits of the bit group while maintaining the bits of each of the different sample strings (s1, s2,...) on the same LSB side or MSB side, respectively, and the bit groups are pulled out in sequence and subjected to encoding as unit processing information in said search step, and in the effective bits information generating step, effective bits information corresponding to the unit processing information is generated, the effective bits information determining that the added dummy bits are not effective and the other bits in the unit processing information are effective. an input step inputting strings of samples including sample strings having a variable length; a unit processing information generating step for generating a sequence of bit groups to be subjected to encoding as unit processing information; an effective bits information generating step of generating effective bits information corresponding to the unit processing information; a search step of obtaining an index of one of the strings of pieces of dictionary information that provides a match, for effective bits of each piece of unit processing information, with a largest number of sequential pieces to be coded in the string of pieces of unit processing information, the effective bits being determined by the effective bits information corresponding to the each piece of unit processing information; and an output step of outputting the index obtained at the search step or a code representing the index; in the unit processing information generating step sample strings (s1, s2,...) having a variable length are converted into a definite-length character string to retain the correlation among or within samples, each character string being composed of one or more bit groups, wherein if the number of bits of a sample is not an integral multiple of a predetermined number of bits matching to the size of pieces of dictionary information registered in the dictionary part, so that residual bits are left at a MSB side or LSB side of the sample, respectively, dummy bits are added to the residual bits from the MSB side or LSB side, respectively, until the number of bits according to the predetermined number of bits of the bit group is reached, so that each sample becomes an integral multiple of the predetermined number of bits of the bit group while maintaining the bits of each of the different sample strings (s1, s2,...) on the same LSB side or MSB side, respectively, and the bit groups are pulled out in sequence and subjected to encoding as unit processing information in said search step, and in the effective bits information generating step, effective bits information corresponding to the unit processing information is generated, the effective bits information determining that the added dummy bits are not effective and the other bits in the unit processing information are effective.