In order to appropriately detect abnormalities for the purpose of surveillance with it being possible to prevent an unnecessary increase in data amount of the monitoring images, a monitoring system includes an image capturing section that captures a moving image of a monitored area, a variation reduced image generating section that generates a variation reduced image by reducing a temporal variation in an image, based on a plurality of moving-image making-up images included in the moving image captured by the image capturing section, a condition storing section that stores thereon a condition which is required to be satisfied by a variation reduced image which is generated by using a plurality of moving-image making-up images included in a moving image which is judged to show an abnormality, a satisfaction judging section that judges whether the variation reduced image generated by the variation reduced image generating section satisfies the condition, an output moving image generating section that, when the satisfaction judging section judges negatively, generates an output moving image which has a lower image quality than when the satisfaction judging section judges positively, based on the moving image captured by the image capturing section, and an output section that outputs the output moving image generated by the output moving image generating section.