To measure roundness errors of cylindrical workpieces and spindle errors of machine tools in on-machine conditions, it is important to separate the roundness error and spindle error from each other. Basically there are two kinds of error separation methods. One is known as the multi-orientation method, and the other is the multi-probe method. Multi-orientations including the step method and the reversal method can separate the spindle error and the roundness error effectively, if the spindle error has good repeatability. Compared with multi-orientation methods, multi-probe methods are more suitable for on-machine measurements, because the repeatability of the spindle error is not necessary. In this paper, we present a new error-separation method using multiple angle probes. In the angular three-probe method, three angle probes are fixed around the workpiece to detect roundness profile and two-dimensional spindle error components simultaneously. The effect of the spindle is canceled in the differential output of the probes and the correct roundness profile can be evaluated from the differential data. In this paper, the principle of the angular three-probe method is described. Experimental results of comparing with the conventional displacement three-probe method are also presented.