A measurement method including a main measurement process Sa in which measurement is performed by rotating a screw in the forward direction with a back-flow prevention valve installed on its tip and a post-measurement process Sb which is performed by rotating the screw in a reverse direction after the main measurement process Sa is finished, the post-measurement process Sb being performed after completing the main measurement process Sa, in which the screw is moved forward in a free rotational state, the rotational state of the screw during the forward movement being monitored, and if the rotation of screw comes to a halt, the screw is rotated in a reverse direction by a specified amount of rotation.