Recently, as elderly people population grows, the burden on caretakers are getting larger. In day care center, caretakers are taking care records aiming to improve care receiver's Quality of Life (QoL). However, in the present situation, it is difficult for caretakers to record care receiver's activity in detail because each care worker needs to take care of several care receivers at the same time and it is a large burden. To reduce the burden of caretakers, many elderly monitoring systems have been proposed so far, but most of them are not effective in the sense that they force care receivers to use dedicated device such as smart phone and/or particular applications that are obtrusive and cumbersome for care receivers. In this paper, we propose a novel elderly monitoring system which can monitor movements/activity of multiple care receivers at the same time by estimating existence area of each of the care receivers, without burdening them. Our proposed system estimates multiple care receivers existence area only using RSSI (Received Signal Strength Indication) of BLE (Bluetooth Low Energy). The feature of our proposed system is that it takes Movable-Beacon and Fixed Scanner style. We have validated the proposed system and confirmed that we can estimate multi-person's existence area at high accuracy using only BLE devices.