To provide a relative attitude measuring apparatus of the front barrel to the rear barrel of a tunnel excavator which can measure surely the relative attitude of the front barrel to the rear barrel without needing to install a laser device between the rear barrel and the front barrel.

This relative attitude measuring apparatus of a rear barrel and a front barrel of a tunnel excavator is equipped with at least three stroke gauges measuring a distance connecting a specified point in a rear barrel 1 and a specified point in a front barrel 2, at least one linear member connecting rectilinearly a first point Q1 in the rear barrel 1 with a second point P1 in the front barrel 2, a displacement gauge which is disposed in the rear barrel 1 or the front barrel 2 and measures displacements in two vertically intersecting directions of the linear member, and an operating device operating the relative attitude of the rear barrel 1 and the front barrel 2, on the basis of measured values of the stoke gauge and the displacement gauge.