The invention relates to a device for treating the hair and to the corresponding application method, the device (2) comprising: —two arms (5, 6) that are able to move relative to one another between a moved-together configuration for treating the hair and a spaced-apart configuration for inserting hair to be treated between said arms, and —a system (18) for applying a product, comprising an applicator member (26) for applying the product, the application system (18) being mounted on one of the arms (5) and being able to move relative to said arm (5) between at least two positions generating, while the device (2) is being used to treat the hair, different respective application pressures of the applicator member (26) on the hair to be treated.