From a viewpoint of CSHKP model, an upward reconnection jet arises when a solar flare occurs, which is expected to make a significant contribution to plasmoid ejection. Observationally (Ohyama & Shibata 1997), it was shown that an eruptive plasmoid had three evolutionary phases (left panel of Figure 2): gradual rising (initial phase), rapid acceleration (intermediate phase), and long-lasting steady rising (final phase). We performed MHD simulations and compare them to the observational result, thereby identifying a possible physical process responsible for each of these phases; that is, a plasmoid starts to rise slowly when a weak resistive process is initiated in a current sheet formed below the plasmoid, which is then accelerated rapidly once fast magnetic reconnection is activated in the current sheet (main phase of the flare), and finally the plasmoid rises at almost constant speed after the upward reconnection jet produces a reverse fast-mode MHD shock wave at the bottom of the plasmoid (Magara, Shibata, & Yokoyama 1997).