Nouns ending in -ail, -eil, -euil, or -ueil are masculine.
The whole family: -ail, -eil, -euil, -ueil. All masculine.
Is appareil masculine or feminine?
l'appareil
The rule behind it
100% of -ail / -eil / -euil / -ueil nouns are masculine
In context
J'ai pointé mon appareil photo sur elle.
I pointed my camera at her.
Je me suis procuré un nouvel appareil photographique.
I got a new camera.
Sais-tu où il a acheté son appareil photo ?
Do you know where he bought his camera?