THz measuring device for measuring a transported, in particular extruded, measuring object, said THz measuring device comprising: one or more THz transceivers (5a, 5b, 5c, 5d) arranged around a longitudinal axis of the measuring space of the THz measuring device, a first mirror means including one or more first deflection mirrors (8a, 8b, 8c, 8d), a second mirror means being arranged offset along the longitudinal axis in relation to the first mirror means, said second mirror means including one or more second deflection mirrors (18a, 18b, 18c, 18d), each THz transceiver (5a, 5b, 5c, 5d) being configured to send a THz transmission beam (7a, 7b, 7c, 7d) along its optical axis, which runs perpendicular to the longitudinal axis, radially inwards towards a first deflection mirror (8a, 8b, 8c, 8d) each, in such a manner that the THz transmission beam (7a, 7b, 7c, 7d) is reflected at the first deflection mirror (8a, 8b, 8c, 8d) and runs along the longitudinal axis as a lengthwise running transmitted beam (17a, 17b, 17c, 17d) and is subsequently reflected at a second deflection mirror (18a,18b, 18c, 18d) each radial in a direction radially outwards as a radial reflected beam (27a, 27b, 27c, 27d) and is deflected, in a direction perpendicular to the longitudinal axis, and, following an inwards reflection, is subsequently reflected back via the second mirror means and the first mirror means towards the respective THz transceiver (5a, 5b, 5c, 5d), said THz transceiver supplying a measuring signal (Sa, SB, Sc, Sd), said THz measuring device being configured to determine one or more of the following properties of the measuring object from the measurement signals of the THz transceivers (5a, 5b, 5c, 5d): - a layer thickness (d) of the measuring object at various locations of the longitudinal axis und/or various locations on the circumference, - a refraction index of the measuring object, - inclusions of air and other substances inside the measuring object - irregular formation of boundary surfaces (2-1, 2-2), and formation of boundary surfaces (2-1, 2-2) of the measuring object that are non-parallel to the longitudinal axis. one or more THz transceivers (5a, 5b, 5c, 5d) arranged around a longitudinal axis of the measuring space of the THz measuring device, a first mirror means including one or more first deflection mirrors (8a, 8b, 8c, 8d), a second mirror means being arranged offset along the longitudinal axis in relation to the first mirror means, said second mirror means including one or more second deflection mirrors (18a, 18b, 18c, 18d), each THz transceiver (5a, 5b, 5c, 5d) being configured to send a THz transmission beam (7a, 7b, 7c, 7d) along its optical axis, which runs perpendicular to the longitudinal axis, radially inwards towards a first deflection mirror (8a, 8b, 8c, 8d) each, in such a manner that the THz transmission beam (7a, 7b, 7c, 7d) is reflected at the first deflection mirror (8a, 8b, 8c, 8d) and runs along the longitudinal axis as a lengthwise running transmitted beam (17a, 17b, 17c, 17d) and is subsequently reflected at a second deflection mirror (18a,18b, 18c, 18d) each radial in a direction radially outwards as a radial reflected beam (27a, 27b, 27c, 27d) and is deflected, in a direction perpendicular to the longitudinal axis, and, following an inwards reflection, is subsequently reflected back via the second mirror means and the first mirror means towards the respective THz transceiver (5a, 5b, 5c, 5d), said THz transceiver supplying a measuring signal (Sa, SB, Sc, Sd), said THz measuring device being configured to determine one or more of the following properties of the measuring object from the measurement signals of the THz transceivers (5a, 5b, 5c, 5d): - a layer thickness (d) of the measuring object at various locations of the longitudinal axis und/or various locations on the circumference, - a refraction index of the measuring object, - inclusions of air and other substances inside the measuring object - irregular formation of boundary surfaces (2-1, 2-2), and formation of boundary surfaces (2-1, 2-2) of the measuring object that are non-parallel to the longitudinal axis. - a layer thickness (d) of the measuring object at various locations of the longitudinal axis und/or various locations on the circumference, - a refraction index of the measuring object, - inclusions of air and other substances inside the measuring object - irregular formation of boundary surfaces (2-1, 2-2), and formation of boundary surfaces (2-1, 2-2) of the measuring object that are non-parallel to the longitudinal axis.