The object of the present invention is to provide a machining time estimation device for reducing the time required for estimating the machining time. The device comprises storage for storing machining program and machining setting, and machining information acquiring unit for acquiring machining information on an operating condition of a machine tool adapted to be controlled on the basis of the machining program and machining setting. The device further comprises varied element extraction unit for extracting an element varied between a plurality of said machining settings, effected block extraction unit for extracting an effected block the machining time is varied on the effect of the varied element, estimated reduction in time calculating unit for calculating on each effected block difference caused by the varied element and calculating estimated difference in time throughout the machining program, and machining time display unit for outputting the estimated difference in time.