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 view showing the state of the skin treatment apparatus installed on a cradle with the arms folded
The broken lines in Figure 1.8 indicate portions of the skin treatment apparatus that form no part of the claimed design.
The portions of the design shown in the color grey in Figure 1.3 and 1.7 are for the purpose of illustrating portions of the skin treatment apparatus and form no part of the claimed design.