A surveillance system (1) includes an area information acquisition unit (101), a position information acquisition unit (102), a candidate determination unit (103), and a notification unit (104). The area information acquisition unit (101) acquires information of a surveillance-desired area. The position information acquisition unit (102) acquires pieces of position information of a plurality of portable terminals (20), each portable terminal performing surveillance using an image capturing unit. The candidate determination unit (103) determines a candidate portable terminal (20) to be moved to the surveillance-desired area from among the plurality of portable terminals (20) based on the acquired pieces of position information of the plurality of portable terminals (20). The notification unit (104) outputs a notification to the candidate portable terminal requesting to move to the surveillance-desired area.