handsome face; beautiful features
Idiomatic phrase literally meaning 'sweet mask', used to describe a man's good-looking face, often with a nuance of charm or gentle attractiveness.
He is popular with women because of his handsome face.
That actor is the owner of a beautiful face.
The phrase combines 甘い (sweet) with マスク (mask, face), metaphorically likening a handsome face to a sweet mask. The exact origin is uncertain, but it has been used since at least the mid-20th century.