A hydraulic tubing support structure in an operating machine including a plurality of hydraulic actuators, comprising: a floor plate formed with a pair of left and right vertically penetrating through holes (32a, 32b); a driver's seat provided on the floor plate; a pair of operating levers provided at both left and right sides of the driver's seat; a pair of left and right operation valves (16, 17) for generating pilot pressures for the plurality of hydraulic actuators in response to an input operation performed on each operating lever; a pair of left and right pump-side tubes (P1, P2) respectively extending from the respective operation valves (16, 17) and guided to below the floor plate through the through holes (32a, 32b); a pair of left and right tank-side tubes (T1, T2) respectively extending from the respective operation valves (16, 17) and guided to below the floor plate through the through holes (32a, 32b); a junction tube for allowing communication of the respective pump-side tubes (P1, P2) guided to below the floor plate through the through holes (32a, 32b) and communication of the respective tank-side tubes (T1, T2) guided to below the floor plate through the through holes (32a, 32b); and a first reinforcement beam extending in a right-and-left direction and fixed to the lower surface of the floor plate, wherein the junction tube is fixed to the first reinforcement beam in a non-contact state with the floor plate characterized in that the first reinforcement beam includes a main body portion extending in the right-and-left direction and a pair of front and rear leg portions standing on this main body portion, upper end parts of the respective leg portions being welded to the lower surface of the floor plate to form a clearance between the main body portion and the floor plate; the main body portion is formed with an internally threaded portion with which a bolt is threadably engageable from below the main body portion; and the junction tube is fixed to the first reinforcement beam by the bolt threadably engaged with the internally threaded portion of the main body portion. a floor plate formed with a pair of left and right vertically penetrating through holes (32a, 32b); a driver's seat provided on the floor plate; a pair of operating levers provided at both left and right sides of the driver's seat; a pair of left and right operation valves (16, 17) for generating pilot pressures for the plurality of hydraulic actuators in response to an input operation performed on each operating lever; a pair of left and right pump-side tubes (P1, P2) respectively extending from the respective operation valves (16, 17) and guided to below the floor plate through the through holes (32a, 32b); a pair of left and right tank-side tubes (T1, T2) respectively extending from the respective operation valves (16, 17) and guided to below the floor plate through the through holes (32a, 32b); a junction tube for allowing communication of the respective pump-side tubes (P1, P2) guided to below the floor plate through the through holes (32a, 32b) and communication of the respective tank-side tubes (T1, T2) guided to below the floor plate through the through holes (32a, 32b); and a first reinforcement beam extending in a right-and-left direction and fixed to the lower surface of the floor plate, wherein the junction tube is fixed to the first reinforcement beam in a non-contact state with the floor plate characterized in that the first reinforcement beam includes a main body portion extending in the right-and-left direction and a pair of front and rear leg portions standing on this main body portion, upper end parts of the respective leg portions being welded to the lower surface of the floor plate to form a clearance between the main body portion and the floor plate; the main body portion is formed with an internally threaded portion with which a bolt is threadably engageable from below the main body portion; and the junction tube is fixed to the first reinforcement beam by the bolt threadably engaged with the internally threaded portion of the main body portion.