A synonymous expression assessment device includes: synonymy assessment means for receiving input of binary relations each of which includes a nominal and a predicate, and assessing whether or not the input binary relations are synonymous using a similarity between input nominals and a similarity between input predicates; and inter-predicate similarity computation means for, when computing the similarity between the input predicates based on a distribution of occurrence frequencies of nominals that are in binary relations to the input predicate in a document set, performing the computation using a distribution of only nominals that are used in the same type of concept as the input nominal.