Automated negotiation has attracted increasing interest and received phenomenal attention in the area of electronic market (e-market). Most of the studies on the automated negotiation focused on the distributive (zero-sum) negotiation, and their effectiveness is only illustrated in a single-issue negotiation between software agent-to-software agent interaction. In this study, we propose an offer strategy model of integrative negotiation for an automated negotiation agent and focus on software agent-to-human interaction. Our offer strategy model is based on the integrative approach and negotiation theory, which emphasize the importance of exchanging information among negotiators and multi-issue negotiation including package offers helping to achieve an integrative (win-win) outcome. In developing this model, we are incorporating negotiation strategy of argumentation-based negotiation and negotiation tactic of multiple equivalent simultaneous offers as an offer strategy to achieve an integrative (win-win) negotiation outcome. We expect that the result from applying the offer strategy model becomes more attractive and persuasive, thus may increase negotiation outcome satisfaction for both economic measure and social-psychological measure.