To provide a polarimeter which is improved in the accuracy of measurement of optical rotation, and a method for calibrating the polarimeter.

This polarimeter is so constituted that linear polarized light transmitted through a sample solution in a sample cell 13, so as for the plane of polarization to be rotated, is made to enter an optical analyzer 14 and that the optical rotation in the sample solution is measured, based on an angle of rotation formed by making the optical analyzer 14 rotate by a hollow motor (electric motor) 15 so that the quantity of light transmitted through the optical analyzer 14 and received by a light-receiving element (light-receiving means) 16 be minimized. Besides, by making the optical analyzer 14 vibrate in a rocking manner by the hollow motor 15 in measuring the optical rotation, the polarimeter makes an angle formed by the axis of transmission of the optical analyzer 14 and the plane of polarization of the linear polarized light vibrate, makes the quantity of light transmitted through the optical analyzer 14 vibrate and performs processing based on the vibrating quantity of light. Moreover, by calibrating the angle of rotation of the hollow motor 15 by using a motor of a higher accuracy than that of the hollow motor 15 the polarimeter is made to perform calibration of measurable optical rotation, based on actual measurement.