Provided is a multi-beam antenna device capable of achieving two independent multi-beam characteristics using a single antenna unit, and enhanced gain. The multi-beam antenna device comprises a first antenna section, a second antenna section, a first Rotman lens section and a second Rotman lens section, which are laminated together in this order to form a planar antenna module. A first multi-beam characteristic is achieved by the first antenna section and the first Rotman lens section, and a second multi-beam characteristic is achieved by the second antenna section and the second Rotman lens section, independently. A Rotman lens in each of the Rotman lens sections is designed such that: β with respect to α is set to satisfy the following relation: β