To provide a method for securely attaching an object on the surface of a sunken or wet object within a short time using an instantaneous adhesive.

The instantaneous adhesive is applied onto the object to be attached and covered with a non-water-permeable sheet before it solidifies, the sheet is removed as soon as the object reaches the adherend underwater, and the surface of the object onto which the adhesive is applied is pressed against the adherend. Alternatively, the object to be attached is soaked into the instantaneous adhesive and kept watertight in a non-water-permeable capsule, the capsule is unsealed as soon as the object reaches the adherend underwater, and the object to which the adhesive is attached is directly pressed against the adherend. The object to be attached is a waterproof strain gauge, and the adherend is a wall of a pilot pore formed on a borehole bottom.