Abstract: An apparatus for measuring trend and plunge of a geologic line feature and an auxiliary apparatus for measuring trend and plunge. The apparatus for measuring trend and plunge includes a rod operable to be disposed parallel to a lineation, a rotation block connected to an end of the rod and being operable to rotate around a central axis of the rod, the rotation block includes a hinge shaft extending in a direction perpendicular to the central axis of the rod, a plate coupled to the hinge shaft of the rotation block so that the plate is rotatable around the hinge shaft, a protractor disposed on the hinge shaft, and a measuring unit disposed on the plate, the measuring unit includes a compass configured to confirm a direction of the rod, thereby measuring the trend when the plate is horizontally disposed.