A watching system, which calculates a fall probability of an imaged person to be fallen using a computer which includes a processor and a memory, includes a trunk extraction unit that receives time-series skeleton information of the imaged person, calculates an angle between a head and a waist of the imaged person based on the skeleton information, extracts the angle as a trunk of the imaged person, calculates the center of the trunk as a trunk center based on trunk information set in advance, extracts a trunk to be reference as a reference trunk from a time-series trunk calculated from the time-series skeleton information, and holds a center of the reference trunk, and a fall probability calculation unit that calculates a distance between a trunk center of the reference trunk and a trunk center of the trunk as a deviation amount, and calculates the fall probability from the deviation amount.