region of the pit section which are evenly distributed across the circumference these support elements 15 include support plates 16 which in a retracted position each form a section of the cylindrical sheath 3 of the horizontal drilling device the support plates 16 can each be extended outward in radial direction by means of a hydraulic cylinder 17 to generate a direct contact of the horizontal drilling device 1 with the wall of the excavation pit 4 to securely support the horizontal drilling device 1 inside the excavation pit 4 the individual components of these support elements 15 are well recognizable in fig3 each of the support plates 16 is connected to a first end of an extension lever 19 via a first pivot joint 18 with the extension lever 19 being in turn rotatingly supported on the housing 2 of the horizontal drilling device 1 by means of a second pivot joint 21 a second end of the extension lever 19 is connected to the head of a piston rod 20 of the hydraulic cylinder 17 an extension or retraction of the hydraulic cylinder 17 thus causes a partial rotation of the extension lever 19 about the pivot joint 21 whereby the respective support plate 16 can be radially extended or retracted again end stops 22 prevent that the support plate 16 enters the inner space defined by the sheath of the housing when retracting the hydraulic cylinder 17 fig2 shows a representation of the entire horizontal drilling device 1 which corresponds to the representation of fig1 in which however a part of the sheath 3 in the excavation pit is removed to show the functional elements arranged therein fig3 to 5 show different views of this section of.