PROBLEM TO BE SOLVED: To provide a plant moisture dynamic state sensor for easily measuring a moisture dynamic state in a fine region of a plant, such as a new branch tip and a carpophore, without placing a load on the plant.SOLUTION: A sensor for measuring a moisture dynamic state in a plant includes: a pair of probes installed by being inserted into a plant; and a support which supports the pair of probes. Each prove, while being installed by being inserted into the plant, has such a length that the tip part can be placed in a conducting vessel and/or a sieve tube of the plant, and has a shaft diameter of 50 μm to 300 μm. Since the probe is just inserted into the plant, a mounting operation is facilitated. Moreover, since the shaft diameter of the probe is small, stress given to the plant can be reduced even if it is installed by being inserted into the plant. Therefore, the sensor can measure the moisture dynamic state in a fine region of the plant immediately after the installation, and can be easil
