We investigated densities of the bean bug, R. pedestris (Alydidae) and three Pentatomidae stinkbug species, Dolycoris baccarum, Nezera antennata and Halyomorpha halys in an experimental field in Suwon, 2018. Three pheromone traps for R. pedestris adults were installed at distances of more than 50 meters from soybean fields. The adults began to be caught from late March. Its mean number increased from early August, and reached a maximum at early September. The fluctuation aspects of adult number caught, however, were different among trapping sites. Soybean and mungbean were sowed at June 21, and all stages of stinkbugs were scouted from July 18 to late September through direct observation. Adults and eggs of R. pedestris were not observed during the vegetative stage of soybean, but observed first at the flowering stage, mainly early August, of reproductive stage. The results indicated that R. pedestris adults invaded into soybean fields at the flowering stage, despite of inhabitation in the surrounding area during the pre-reproductive stage of soybean. Adults of only D. baccarum in Pentatomid stinkbugs were found at the vegetative stage of soybean. Densities of R. pedestris were compared between two mungbean cultivars, which those seeds have been known to be resistant and susceptible to feeding of the bean bug, respectively. The densities of the third and fifth instar nymphs were higher on the susceptible cultivar than on the resistant cultivar, but densities of egg, adult, and the first and second instar nymphs were not significantly different between the two cultivars.