DETERIORATION CONDITION DETERMINATION METHOD AND DETERIORATION CONDITION DETERMINATION DEVICE

A degradation state determination method is for a degradation state determination apparatus to determine a degradation state of a tire mounted on a vehicle based on a color of an indicator attached to the tire. The method includes determining the degradation state of the tire, using a degradation determination model that takes an amount of a degradation factor that causes the tire to degrade as input and outputs an index of the degradation state, based on a color change database, including data indicating a relationship between a change in color of the indicator and the amount of the degradation factor, and a color component extracted from an image of the indicator attached to the tire, and proposing, based on the determined degradation state of the tire, an option that is at least one of a method and a product that are selectable when retreading the tire (S44 to S48).