Three-dimensional structures of reconnection jets are investigated by hybrid simulations. Magnetic reconnection is initiated by ad-hoc anomalous resistivity, which is uniform in the cross-tail direction but localized within the meridian plane. At the interface between the reconnection jet and the pre-existing plasma sheet ahead of it, the reconnected field lines are piled up and the plasma density is enhanced by compression. The interface becomes unstable to an interchange instability and deforms itself into a wavy shape. In the non-linear growth phase, the wavy perturbations grow into magnetic bubbles into which the field lines are converged and the bubbles move faster than the other parts. It is suggested that this instability can generate localized channels with a cross-tail extent of a few RE, in which plasma and magnetic field transports are achieved, and thus may well be related to the formation of the bursty bulk flows in the magnetotail.