An electric current layer structure characterized not only by electron dynamics but by ion dynamics is demonstrated in collisionless driven reconnection by means of the two-dimensional full-particle simulation in an open system for a large mass ratio of ion to electron. The current density profile along the inflow direction consists of two parts in a steady state. One is a sharp peak characterized by electron dynamics. The other is a low shoulder characterized by ion dynamics. The separation of the shoulder from the sharp peak is revealed by virtue of the large mass ratio calculation, Mi/Me=200. The shoulder is caused by a two-peak structure of plasma density. The ion meandering motion gives rise to a strong breaking of ion frozen-in constraint and forms the two-peak structure. An electrostatic field generated by the breaking of the constraint causes the ExB drift of electron, and thus controls the current density profile.