PURPOSE:To execute auto tuning with high accuracy by constituting the titled device so that a tuning point detected first by auto tuning is not set as a just point as it is, but the just point is determined by inspecting a tuning point of its vicinity. CONSTITUTION:In an auto tuning device, when a search is started in order to determine a just point, a tuning point discriminating means 204 of a microcomputer 20 discriminates whether an output SD of a comparing circuit 18 has become a low level or not, and discriminates whether it is a tuning point or not. Subsequently, a result of its discrimination is supplied to a just point discriminating means 205. The just point discriminating means 205 supplies a control signal to a search means 201, supplies an N value change signal to an N value changing means 202, and determines the just point.
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