To solve the problems that a conventional soil support force measuring method using a plate loading test device is large-scaled and takes long time and a high cost to measure soil support force, and immediate coping cannot be performed when the abnormal change of the soil support force is found during an actual construction.

By using a small-sized and light-weight soil support force test device which includes a chair 7 that a person can sit in a sitting state, a piston 2, pressure means 3, pressure measuring means 4, an approach body 5 and approach amount measuring means 6 and which can be carried manually, the soil support force is measured in a short time and at a low cost. Also, by executing a civil engineering/building construction after measuring the soil support force in a construction site of the civil engineering/building construction or while measuring the soil support force, retesting is performed and measures are taken immediately when the abnormality of the soil support force is found during the execution of the construction.