An antenna and an antenna apparatus for vehicle that can achieve reduction in size are provided. The antenna includes a dielectric body, a radiation conductor disposed on a first principal surface side of the dielectric body, and a ground conductor disposed on a second principal surface side of the dielectric body. The ground conductor is a planar conductor disposed within a rectangular region having a length LG1 in a first direction and a length LG2 in a second direction. When the ground conductor is divided into a first region and a second region, the ground conductor includes a slit that starts extending toward the inside of the ground conductor starting from an outer edge of the ground conductor in the first region.