An abnormality judging device comprising: detecting means which detects a physical quantity generated from a revolving tire, for each of the tires; extracting means for extracting a specific signal from signals corresponding to the physical quantity detected by the detecting means, for each of the tires; and judging means for judging that the tire is abnormal when a difference value between two signals extracted by the extracting means exceeds a predetermined threshold, characterised in that: the judging means judges that the tire is abnormal in a case where any one of the difference value between signals corresponding respectively to two tires rotatably and pivotally supported on the same shaft and the difference value between a signal corresponding to a front tire and a signal corresponding to a rear tire provided in a traveling direction of the front tire, out of the signals extracted by the extracting means, exceeds the predetermined threshold; in that the judging means judges that the tire is abnormal in a case where the difference value between the signals corresponding respectively to the two tires rotatably and pivotally supported on the same shaft, out of the signals extracted by the extracting means, exceeds the predetermined threshold at the time when a vehicle is running at a constant speed or is in the course of acceleration or deceleration; and in that the judging means judges that the tire is abnormal in a case where the difference value between the signal corresponding to a front tire and the signal corresponding to a rear tire provided in the traveling direction of the front tire, out of the signals extracted by the extracting means, exceeds the predetermined threshold at the time when a vehicle is running at a constant speed or is turning. detecting means which detects a physical quantity generated from a revolving tire, for each of the tires; extracting means for extracting a specific signal from signals corresponding to the physical quantity detected by the detecting means, for each of the tires; and judging means for judging that the tire is abnormal when a difference value between two signals extracted by the extracting means exceeds a predetermined threshold, characterised in that: the judging means judges that the tire is abnormal in a case where any one of the difference value between signals corresponding respectively to two tires rotatably and pivotally supported on the same shaft and the difference value between a signal corresponding to a front tire and a signal corresponding to a rear tire provided in a traveling direction of the front tire, out of the signals extracted by the extracting means, exceeds the predetermined threshold; in that the judging means judges that the tire is abnormal in a case where the difference value between the signals corresponding respectively to the two tires rotatably and pivotally supported on the same shaft, out of the signals extracted by the extracting means, exceeds the predetermined threshold at the time when a vehicle is running at a constant speed or is in the course of acceleration or deceleration; and in that the judging means judges that the tire is abnormal in a case where the difference value between the signal corresponding to a front tire and the signal corresponding to a rear tire provided in the traveling direction of the front tire, out of the signals extracted by the extracting means, exceeds the predetermined threshold at the time when a vehicle is running at a constant speed or is turning. the judging means judges that the tire is abnormal in a case where any one of the difference value between signals corresponding respectively to two tires rotatably and pivotally supported on the same shaft and the difference value between a signal corresponding to a front tire and a signal corresponding to a rear tire provided in a traveling direction of the front tire, out of the signals extracted by the extracting means, exceeds the predetermined threshold; in that the judging means judges that the tire is abnormal in a case where the difference value between the signals corresponding respectively to the two tires rotatably and pivotally supported on the same shaft, out of the signals extracted by the extracting means, exceeds the predetermined threshold at the time when a vehicle is running at a constant speed or is in the course of acceleration or deceleration; and in that the judging means judges that the tire is abnormal in a case where the difference value between the signal corresponding to a front tire and the signal corresponding to a rear tire provided in the traveling direction of the front tire, out of the signals extracted by the extracting means, exceeds the predetermined threshold at the time when a vehicle is running at a constant speed or is turning.