A strain detector includes an insulating substrate, a power electrode, output electrodes and a ground electrode which are disposed over the insulating substrate, a strain-resistance element provided over the insulating substrate and coupled to the power electrode, the output electrodes and the ground electrode, a protective layer over the strain-resistance element, a frame ground electrode. The insulating substrate includes a stainless steel board, a protective coat on the stainless steel board, and an insulating layer on the protective coat. The frame ground electrode is provided over the stainless steel board and electrically coupled to the stainless board.
