A clogging degree deciding method for a dryer, which can accurately determine a clogging degree of an air passage, even when there is an influence of external environments, is disclosed. The clogging degree deciding method includes reading information as to clogging of an air passage, and displaying a clogging degree of an exhaust duct or a clogging degree of a filter in accordance with the read clogging information. The clogging information includes an ON/OFF duty ratio of a temperature control member. The displaying step includes comparing a difference between two ON/Off duty ratios finally stored with a filter-clogging determination reference value, and determining the clogging degree of the filter, based on a result of the comparison. Accordingly, it is possible to provide the clogging degrees of the exhaust duct and filter to the user.