To easily and accurately measure the adhesion strength of a minute conductive pad of a wiring board for an area array package such as a BGA(ball grid array).

The tip of a contact tool 3 is brought into contact with the side surface of a minute conductive pad 2 (for example, a diameter is 300 μm) being formed on an insulation substrate 1 such as a glass cloth substrate impregnated with an epoxy resin, and a press force F is applied in parallel with the surface of the insulation substrate 1 by means of the tool 3. Then, the press force is gradually increased, and the press force when the conductive pad 2 is released from the surface of the insulation substrate 1 is measured by a load sensor. When the thickness of the conductive pad 2 is thin and it is difficult to add the press force by bringing the contact tool 3 into contact with the conductive pad 2, a solder projection 4 of the same diameter is stuck and formed on the conductive pad 2, and the contact tool 3 is brought into contact from the side surface of the conductive pad 2 to that of the solder projection 4 to apply a press force.