1. An operation assisting apparatus that estimates a function whose execution is intended by a user based on a history of user operations for selecting an option displayed on a menu screen having a hierarchical structure, and provides an operational assistance based on a result of the estimation, said apparatus comprising: an option-function distance storage unit in which a semantic distance indicating a degree of a relation between each of the options displayed on the menu screen and each of a plurality functions positioned at an end in the hierarchical structure of the menu screen is stored; an estimation unit configured to estimate a probability that each of the functions is the function desired by the user, based on: a semantic distance between a word that describes characteristics of a selection option selected by the user and a word that characterizes each of the functions; and a semantic distance between a word that describes characteristics of an unselected selection option that has been selectable but not selected and a word that characterizes each of the functions; and an operational assistance determination unit configured to determine, based on the result of the estimation, a detail of an output for the operational assistance such that functions with higher probability are more likely to be selected.