Real-time　property　is　a　fundamental　requirement　for　a　practical　robot　system.　For　this　purpose,　this　article　proposes　an　implementation　architecture　of　robot　SLAM　by　adopting　two　parallel　threads　processing.　Since　the　dominant　factor　which　determines　the　computational　complexity　is　the　employed　particle　number,　two　distributed　threads　with　different　particle　set　size　are　executed　simultaneously.　Conventional　PF-SLAM　algorithm　occupies　one　of　threads,　and　the　other　thread　which　hires　more　particles　is　activated　whenever　robot　has　significant　motion　changes.　Advantages　of　this　presented　idea　are　validated　by　experiment　carried　on　Pioneer　robot.