1. A non-transitory computer readable recording medium in which a compressed inverted index is recorded, the compressed inverted index being a data structure storing postings, for every indexing term in a document set, where the document set is searchable by referencing the compressed inverted index, including a plurality of documents respectively assigned identification numbers, each posting having an identification number of a document in which the indexing term occurs, a number of occurrences of the indexing term in the document and information indicating an end of a byte sequence representing the identification number, the indexing term being defined as either a word or a plurality of contiguous letters and the number of occurrences of the indexing term being stored in a frequency field of the posting corresponding to the identification number of the document, wherein, in the compressed inverted index, the identification number of a document in each posting is represented by a byte sequence of variable length including an indicator of an end of the byte sequence, wherein the number of occurrences from 1 to (2 w −1) is represented by w bits within the byte sequence where w is a given integer of not less than 1 and not more than 8, and wherein the number of occurrences greater than or equal to 2 w is represented by an additional byte sequence including another indicator of an end of the byte sequence.