Translation guide
Describes a facial expression that is serious, composed, or not showing amusement, often in contrast to a lighthearted or drunk state.
The most common meaning: a face that shows no amusement, is calm and serious, often when others are laughing or joking.
Literally 'serious face'. Used when someone is not joking or is being earnest. Very natural and common.
He told a joke with a straight face.
Specifically refers to a face that does not show signs of intoxication, or the act of looking sober when one is actually drunk.
Uses シラフ (sober, not drunk). Directly means 'sober face'. Common in contexts of drinking.
真面目な顔 is the most general 'serious/straight face'. 澄ました顔 often implies a deliberate composure, sometimes with a hint of feigned innocence. 涼しい顔 emphasizes coolness under pressure, as if nothing bothers you.
to lie with a straight face
A composed, unruffled face, sometimes with a nuance of acting innocent or pretending nothing happened.
She sat there with a composed face.
Literally 'cool face'. Implies calmness and composure, often when one should be embarrassed or flustered.
He keeps a straight face even when he makes a mistake.
He drank a lot of beer with a sober face.
Plain descriptive phrase: 'face that is not drunk'. Less idiomatic but clear.
He had a sober face, but actually he had drunk quite a lot.
to pretend not to know with a composed face
He keeps a cool face even when scolded.