Provided is a hairstyling apparatus (I) including a portable treatment unit (2) provided with two arms (3, 4) arranged to form a clamp provided with two surfaces (5, 6) disposed opposite one another and enabling a lock of hair to be clamped therebetween. The portable treatment unit includes steam-diffusion means (7) arranged to diffuse steam from a first (5) of the two surfaces towards the second (6) of the two surfaces. The apparatus includes means (9, 10) for confining the diffused steam, between the two surfaces (5, 6) placed one against the other.