The ornamental design for a skintreatment apparatus, as shown and described.
1. Skin treatment apparatus
1.1 : Perspective
1.2 : Front
1.3 : Back
1.4 : Left
1.5 : Right
1.6 : Top
1.7 : Bottom
1.8 : Reference
The broken line showing in figure 1.7 and the broken line showing of the five circular elements in figures 1.1, 1.2, 1.4 and 1.8 depict portions of the skin treatment apparatus that form no part of the claimed design. The broken line showing of a stand in figure 1.8 depicts environment that forms no part of the claimed design.
The bottom of the claim in Fig. 1.7 inside the solid line forms no part of the claimed design.