A viscometer, comprising: a motor having a driving shaft to be a driving source fixed to a chassis; a needle shaft; a spring configured to transmit a driving power of the motor to the needle shaft; a spindle holder, provided on the lower end side of the needle shaft, to which a spindle is attached to be detachable; and a phase difference detection unit (17, 18, 19, 20) configured to detect a rotational phase difference between the driving shaft and the needle shaft; wherein when the spindle attached to the spindle holder is immersed into a sample liquid and the motor is driven, the spring is displaced due to a reaction torque caused by a resistance due to a viscosity of the sample liquid with respect to the spindle, the rotational phase difference between the driving shaft and the needle shaft is detected in a state where a torque caused by a recovering force of the displaced spring and the reaction torque are balanced, and a viscosity of the sample liquid is determined according to the detected rotational phase difference; characterized in that the motor is a hollow shaft motor having a hollow driving shaft in a hollow cylindrical shape penetrating through the motor along a rotational axis, the needle shaft is provided to be piercing through the hollow driving shaft of the hollow shaft motor, having an upper end side supported to be rotatable by the chassis and a lower end side supported to be rotatable by a lower end side of the hollow driving shaft, such that the hollow shaft motor is located between the upper end side of the needle shaft and the lower end side of the needle shaft; and the rotational phase difference is detected between the hollow driving shaft and the needle shaft. a motor having a driving shaft to be a driving source fixed to a chassis; a needle shaft; a spring configured to transmit a driving power of the motor to the needle shaft; a spindle holder, provided on the lower end side of the needle shaft, to which a spindle is attached to be detachable; and a phase difference detection unit (17, 18, 19, 20) configured to detect a rotational phase difference between the driving shaft and the needle shaft; wherein when the spindle attached to the spindle holder is immersed into a sample liquid and the motor is driven, the spring is displaced due to a reaction torque caused by a resistance due to a viscosity of the sample liquid with respect to the spindle, the rotational phase difference between the driving shaft and the needle shaft is detected in a state where a torque caused by a recovering force of the displaced spring and the reaction torque are balanced, and a viscosity of the sample liquid is determined according to the detected rotational phase difference; a needle shaft; a spring configured to transmit a driving power of the motor to the needle shaft; a spindle holder, provided on the lower end side of the needle shaft, to which a spindle is attached to be detachable; and a phase difference detection unit (17, 18, 19, 20) configured to detect a rotational phase difference between the driving shaft and the needle shaft; wherein when the spindle attached to the spindle holder is immersed into a sample liquid and the motor is driven, the spring is displaced due to a reaction torque caused by a resistance due to a viscosity of the sample liquid with respect to the spindle, the rotational phase difference between the driving shaft and the needle shaft is detected in a state where a torque caused by a recovering force of the displaced spring and the reaction torque are balanced, and a viscosity of the sample liquid is determined according to the detected rotational phase difference;