This paper presents a new autocollimator that can simultaneously detect the three-axis angular error motions (pitch, yaw, and roll errors) of a precision linear stage. A collimated laser beam from a laser diode is projected onto a grating reflector mounted on the stage. The reflected 0th-order diffracted beam is received by an autocollimation unit, which consists of a collimator objective and a quadrant photodiode, for detecting the pitch and yaw errors. The reflected 1st-order diffracted beam is received by another autocollimation unit for detecting the roll error. Experiments were carried out to evaluate the basic performance of the prototype sensor.