Magnetic　flux　leakage　(MFL)　sensors,　with　their　compact　configuration　and　high　sensitivity　to　small　defects,　have　attracted　much　attention　in　recent　years　for　the　non-destructive　testing　of　ferromagnetic　structures.　Tunnel　magneto-resistive　(TMR)　devices　have　superior　performances　in　sensitivity　and　linear　operation　range　over　conventional　magneto-resistive　devices.　In　this　paper,　a　commercial　TMR　device　is　employed　for　developing　an　electromagnet-based　MFL　sensor.　The　electromagnet　magnetizer　includes　Helmholtz-like　coils　together　with　a　custom-made　magnetic　shield.　The　orthogonal　test　method　is　applied　to　aid　the　structural　parameter　optimization　to　the　magnetizer　based　on　the　finite　element　analysis　results　of　magnetic　field　distribution.　In　this　study　a　prototype　of　a　TMR-based　MFL　sensor　is　developed,　and　its　performances　on　detecting　various　types　of　defects　are　tested　on　a　scanning　apparatus.　The　experimental　results　show　that　the　MFL　signal　induced　by　a　blind　hole　with　dimensions　of　0.3　mm　in　both　depth　and　diameter　is　detectable.　In　addition,　two　adjacent　notches　located　more　than　2.0　mm　from　each　other　can　be　clearly　distinguished　from　the　received　MFL　signal.　The　detectable　angular　detection　range　for　a　single　TMR　device　is　estimated　as　52　degrees　in　the　tested　linear　shaft　rod.　The　consistency　between　the　simulated　and　received　MFL　signal　induced　by　a　row　of　notches　inspires　confidence　in　the　proposed　sensor　design　method,　which　in　the　future　can　be　transplanted　for　TMR-based　sensor　array　design.　Finally,　the　TMR-based　MFL　sensor　is　used　for　detecting　a　flaw　of　a　single　broken　wire　with　a　diameter　of　0.5　mm,　and　the　induced　MFL　signal　can　be　clearly　recognized　from　the　oscillation　signal　that　is　generated　by　the　twisted　rope　surface.　Therefore,　the　presented　TMR-based　MFL　sensor　has　great　potential　for　steel　wire　rope　inspection　with　enhanced　sensitivity　to　small　defects,　and　it　is　capable　of　being　integrated　into　production　lines　due　to　its　compact　configuration.