An index value assignment device comprises: a selection unit that prompts a user to select, from a sentence, one or more words that the user feels to have a same degree of a predetermined index value with respect to one or more first words for which the index value is known; a validation unit that validates the selection result by the user on a basis of the index value of a second word for which the index value is known from among the one or more words included in the selection result; and a determination unit that determines the index value with respect to a third word for which the index value is unknown from among the one or more words selected by the user, on a basis of the index value of the first word according to the selection result for which the selection result is determined to be valid. Consequently, the efficiency of assigning word familiarity is increased.