The heating efficiency of a negative theta-pinch with reversed bias field is studied by comparing it with that of an ordinary theta-pinch. For this purpose, a high-voltage Z-discharge pre-heat system with short current duration was developed, and by using the highly ionized pre-heat plasma with good reproducibility as the initial plasma, a comparison with the heating in negative and ordinary theta-pinches was carried out. The plasma energy and ion temperature were measured by a magnetic probe and a fast-neutral-particle detector. These measurements show that the heating efficiency in the negative theta-pinch is comparable to that in the ordinary theta-pinch with reversed bias field. Accordingly, the negative theta-pinch is an ideal method of producing and confining energetic plasma in the reversed-field configuration (RFC).