A somewhat playful or figurative expression for one's facial features, treating the face as a set of tools or equipment. Not a clinical term.
His facial features are well-proportioned, like a model.
A compound of 顔 (face) + の (possessive particle) + 道具 (tool, implement), literally 'tools of the face'. The exact origin is uncertain, but it is a figurative phrase treating facial features as equipment.