Two parallel in-plane-gated (IPG) wires are coupled by a ballistic window. The ballistic window is rectangular, and the four terminals have a different arrangement from the usual fourfold-symmetry structures (such as a wire cross) where alternate terminals face each other. The ballistic coupling is achieved between two parallel wires by a sideways component but not by a straightforward component, and the four-terminal resistance (or transfer resistance) becomes negative at zero magnetic field. The amount of a sideways ballistic component is sensitive to a subband depopulation in each wire. The modulation of a sideways ballistic component results in a distinct oscillation in the four-terminal resistance as a function of the IPG voltage. The magneto-depopulation of one-dimensional subbands in each wire is also clearly observed in this system.