1. An information conversion device comprising: a memory; and a processor coupled to the memory, wherein the processor executes a process comprising: generating a conversion rule for converting a feature quantity vector into a binary string that is longer than a predetermined bit length; converting each of the feature quantity vectors into a binary string by using the conversion rule generated at the generating; calculating importance levels of the respective bits in the binary strings based on a distance of the feature quantity vectors; correcting the conversion rule into one that converts each of the feature quantity vectors into a binary string having the predetermined bit length based on the calculated importance levels; and changing the feature quantity vectors into a binary string having the predetermined bit length by using the conversion rule corrected at the correcting.