An inertial input apparatus with six-axial detection ability, structured with a gyroscope and an acceleration module capable of detecting accelerations of X, Y, Z axes defined by a 3-D Cartesian coordinates, which is operable either being held to move on a planar surface or in a free space. When the inertial input apparatus is being held to move and operate on a planar surface by a user, a two-dimensional detection mode is adopted thereby that the gyroscope is used for detection rotations of the inertial input apparatus caused by unconscious rolling motions of the user and thus compensating the erroneous rotations, by which the technical disadvantages of prior-art inertial input apparatuses equipped with only accelerometer can be overcame and thus control smoothness of using the input apparatus is enhanced.