A mechanical quantity measuring device (100) includes a semiconductor substrate (1) attached to a measured object so as to indirectly measure the mechanical quantity acting on the measured object; a measuring portion (7) capable of measuring a mechanical quantity acting on the semiconductor substrate (1) at a central part (1c) of the semiconductor substrate (1); and plural impurity diffused resistors (3a, 3b, 4a, 4b) forming a group (5) gathering closely to each other in at least one place, on an outer peripheral part (1e) outside the central part (1c) of the semiconductor substrate (1). The plural impurity diffused resistors (3a, 3b, 4a, 4b) forming one of the group (5) are connected to each other to form a Wheatstone bridge (2a, 2b). Thus, the mechanical quantity measuring device (100) can securely detect its own exfoliation.