To provide a communication area forming device of an electronic key system, which eliminates the number of antennas of a communication master and also secures the position detecting accuracy of an electronic key.

A vehicle transmitter 10 as a vehicle transmitting antenna of smart communication is a biaxially integrated antenna including a pair of coil-bar antennas 16a, 16b with their antenna axes orthogonal with each other. For verification outside the vehicle, only the first coil-bar antenna 16a is independently transmitted to form a first communication area E1, and then the coil-bar antennas 16a, 16b are transmitted simultaneously in the same phase to form a third communication area E3. Then, the coil-bar antennas 16a, 16b are transmitted in a reversed phase simultaneously to form a fourth communication area E4, thus forming communication area outside the vehicle around the vehicle. For verification inside the vehicle, only the second coil-bar antenna is independently transmitted to form a second communication area E2, forming communication area inside a vehicle in the vehicle 1.

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