This work is based on one of the new observational findings by Yohkoh, which is a hard X-ray loop-top source formed over a soft X-ray flaring loop in a compact (impulsive) flare (Masuda et al. 1994; left panel in Figure 1). In order to clarify the generation mechanism of this loop-top source, we performed a pair of two-dimensional magnetohydrodynamics (MHD) simulations to reproduce relevant dynamic processes explained by the so-called CSHKP model, a famous solar flare model based on magnetic reconnection. We found that a plasma jet originating from a reconnection point collided with an underlying closed loop to produce a standing fast-mode MHD shock wave, behind which a hot and dense source was formed and maintained (Magara et al. 1996; right panel in Figure 1). The temperature of this source is consistent with that derived from the hard X-ray data (about hundred million degrees) when thermal radiation with a realistic value of plasma β (~ 0.01) is assumed (Magara 1998). On the basis of these results, we explained that differences in appearance between short-lived compact flares (impulsive flares) and long-duration-event flares (LDE flares) may originate from the efficiency of the magnetic reconnection operated above the soft X-ray flaring loop (Magara et al. 1996).