An antenna element is formed by providing a radiation electrode on a base member made of a dielectric material. To protect the antenna element from external impact, a void is formed between a housing and the antenna element. This void is filled with a solid member. The relative permittivity of the solid member is equal to or higher than the relative permittivity of the housing, and equal to or lower than the relative permittivity of the base member. The solid member is formed as an elastic member.