Adult numbers of the maize weevil, Sitophilus zeamais Motschulsky, were investigated using pheromone traps in five low-temperature grain storage warehouses in the Kanto Plain, to confirm the effectiveness of the pheromone traps and observe the change in the numbers of adults caught. Pheromone traps and sticky traps were placed in the storage rooms and working areas of each warehouse and replaced with new ones monthly. Bait traps were also used in three warehouses. Large numbers of adult S. zeamais were caught in the traps from April to December. The number of adults caught by pheromone traps was greater than that that caught by sticky traps at all the investigation sites in most months. In pheromone traps, up to 427 adults were caught in one trap, while in bait traps, up to 247 adults were caught in one trap. In two warehouses, the number of adults trapped markedly decreased during the investigation period due to improvements made to storage conditions, but no such trend was apparent in the other three warehouses.