Structure formation and plasma instabilities in collisionless driven reconnection are investigated by three-dimensional electromagnetic (EM) particle simulation in an open system. In the early period, the lower-hybrid drift instability is excited in the periphery of the current layer. In the intermediate period, magnetic islands are created in the downstream due to magnetic reconnection, and they become unstable against a kink instability. In the late period, after the magnetic islands go out through the boundary, a wide, thin current sheet is generated and a low-frequency EM mode is excited in the central region. This mode has a frequency comparable to the ion gyration frequency, and thus it is considered to be the drift kink instability.