Disclosed is an antenna device for an electronic device including a first housing and a second housing rotatably coupled to the first housing about a hinge axis. The antenna device may include: a radiation conductor disposed in the first housing; and a reflection member disposed adjacent to the radiation conductor in the first housing. Radio waves transceived by the radiation conductor are radiated via the reflection member. Also disclosed is an electronic device including the antenna device. The antenna device and the electronic device including the same may be variously implemented according to embodiments.