1. A three-dimensional profile measurement apparatus using the amplitude of a projection grid, the apparatus comprising: a pattern projection unit for projecting a pattern of the projection grid onto an object to be measured having an arbitrary height; an image acquisition unit having an image sensor for acquiring a pattern image projected onto the object; a focal position movement unit for adjusting the focal position between the pattern projection unit and the image acquisition unit so as to obtain the vivid image of the pattern of the projection grid projected onto the object; a position sensor for detecting the quantity of the focal position moved; a controller for receiving the pattern image of the projection grid acquired by the image sensor and a signal from the position sensor detecting the quantity of the focal position moved; and a calculation unit for calculating the height of the object by calculating the image of the image sensor inputted to the controller and the position input signal received from the position sensor.