This letter proposes a new concept of a compact multidirection-beam antenna-in-package (AiP) for mobile devices. The AiP is the first integration of three vertically polarized millimeter-wave endfire horn antennas and a broadside horn antenna on a single substrate to cover four directions. The antennas are able to connect to radio frequency integrated circuits (RFICs) situated in the cavity at the backside of the substrate using bond wires. The size of the fabricated AiP is 6 mm x 6 mm x 1.5 mm (=1.2 lambda(0) x 1.2 lambda(0) x 0.3 lambda(0)) including 0.3 mm thickness of RFICs. The impedance bandwidth (vertical bar S-11 vertical bar < -15 dB) fully covers the 60 GHz band (57-66 GHz). Themeasured boresight gain of the endfire antenna and the broadside antenna is 5 dBi at 57 GHz and 6.3 dBi at 60 GHz, respectively.