Provided is an internal antenna device in such a form as a door handle for a smart entry system and an electronic key that can provide a metallic appearance similar to that of a metallic plating while avoiding a loss in the antenna output and ensuring a stable communication. A metallic thin film is deposited on a surface of an outer cover (9) that receives an antenna of the internal antenna device by sputtering. Cr (chromium) may be selected for the sputtering target, and the film thickness may be in the range of 0.05 .mu.m to 0.20 .mu.m to produce the appearance of a metallic surface. A double layer structure may be used by forming a coating consisting of acrylic urethane paint and having a thickness of 5 .mu.m to 50 .mu.m on the metallic film (16) to protect the metallic film (16) on the surface of the outer cover (9).