A wide-band loop antenna consists of a main loop antenna conductor and a sub-loop antenna conductor. The main loop antenna conductor is provided on a dielectric plate to extend from one terminal of a pair of feed terminals to another one of the terminals so as to form a one-turn open loop. The loop antenna conductor is provided on the dielectric plate so as to extend along the main antenna conductor to provide a one-turn open loop and is connected to the pair of feed terminals to constitute a synthesized antenna together with the main antenna conductor. Short-circuting conductors are provided to connect the main antenna conductor with the sub-antenna conductor for shifting a resonance frequency of the synthesized antenna outside the operating band to obtain a wide-band frequency characteristic. In a modification, the sub-antenna conductor forms a closed loop serving as a parasitic antenna which improves an impedance characteristic of the main antenna conductor.