A blast furnace slag level estimation method and blast furnace slag level estimation apparatus can estimate the liquid level of slag to a high degree of accuracy. An operation guidance method, method of producing hot metal, and operation guidance apparatus also provide guidance for the operation of a blast furnace based on a highly accurately estimated liquid level of slag. The blast furnace slag level estimation method includes a step (S2) of calculating a liquid level of melt containing slag for each region in a plurality of regions separated by a low permeability zone, using a physical model that takes at least one of hot metal tapping rate, slag tapping rate, hot metal production rate, and slag production rate as an input and that is based on a mass balance assuming existence of the low permeability zone with poor permeation of slag at a bottom of a furnace.