  Basic properties of relativistic magnetic reconnection in electron-positron
pair plasmas are investigated by using a particle-in-cell (PIC) simulation. We
first revisit a problem by Hesse & Zenitani (2007), who examined the kinetic
Ohm's law across the X line. We formulate a relativistic Ohm's law by
decomposing the stress-energy tensor. Then, the role of the new term, called
the heat-flow inertial term, is examined in the PIC simulation data. We further
evaluate the energy balance in the reconnection system. These analyses
demonstrate physically transparent ways to diagnose relativistic kinetic data.
