PURPOSE: To obtain a flexion measuring device which can be applied even in the water or when no stable point is available by measuring the level depth difference within the linking tube which bends along with the long beam and thus measuring the flexion amount at each part of the long beam.

CONSTITUTION: Linking tube A made of the synthetic resin or the like is attached in a body to long beam B to bend together with B. Tube A consists of vertical tube 1 plus upper and lower horizontal tubes 2 and 3 with a fixed space between them, and contains liquid W like the water or the like inside. Level gauge 4 is inserted within tube 1, and orifice 5 is provided within tube 3 to control the movement W. Thus the signal of the liquid level height detected by gauge 4 is transmitted to analysis recording part C. And the reference water level such as the liquid level height at the long beam support part plus the liquid level depth difference to the liquid level height at each measuring point are calculated at operation part 7 and via amplifier 6 to be recorded to recorder 8. In such way, the flexion amount can be measured easily even in the water or when no stable point is available.