An inexpensive optical measurement device for spindle error measurement, which has three degrees of freedom (3DOF) and is integrated with the Internet of things (IoT), is presented. The device uses an artificial standard sphere, which is set on the spindle to be measured, and two optical measurement modules. Each module includes an aspherical lens, a laser diode, a beam splitter and a quadrant position-sensing detector, and the autocollimator principle of measurement is used. After the calibration of the device, the residual error and resolution are about 1 and 0.1 µm, respectively. The experiment results show errors of measurement, caused by the roughness of the standard sphere, as periodic noise with an amplitude of 10 µm. After the noise has been eliminated, the error motion of the spindle, which includes radial, axial, and synchronous and asynchronous errors, can be observed. The proposed device can also be used for the measurement of spindle thermal expansion.