In an abnormality detection system of a mobile robot, it is configured such that it is self-diagnosed whether the quantity of state is an abnormal value, or whether at least one of the internal sensor, etc., is abnormal and when an abnormality is self-diagnosed, abnormality information affixed with a time on which the abnormality occurred is outputted to be stored in an internal memory and in an external memory. With this, it becomes possible to improve the reliability of abnormality detection of the mobile robot and by storing the information affixed with a time on which the abnormality occurred, it becomes possible to ascertain accurately the course of events leading up to the abnormality. It is further configured such that in addition to a time on which the abnormality occurred, the information is stored in an external memory together with a parameter indicative of the quantity of state.