DISTANCE-MEASURING DEVICE AND DISTANCE-MEASURING METHOD

To provide a distance measuring device and a method for measuring a distance, being capable of simply and quickly measuring a distance from an opening of a reaction tube to a solid in a granular shape filled in the reaction tube.A distance measuring device 10 includes a measuring member 300 holding a length measuring instrument 100 and at least one rail member 200 (base member) on which the measuring member is movably disposed. When a straight line parallel to a direction in which the measuring member disposed on the base member moves is defined as a reference line, an angle formed by a straight line parallel to an axial length direction D2 of a reaction tube 910 and the reference line, which are on an identical plane, is constant for the plurality of reaction tubes disposed side by side along the reference line. A measurement direction D1 of the length measuring instrument is parallel to the axial length direction of the reaction tube in a state where the measuring member is disposed on the base member. The measuring member is disposed on the base member to be able to sequentially move from a position P1(P2) where a distance of one reaction tube is measured to a position P2(P3) where the distance of another reaction tube is to be measured.