The sensor has the self-detecting probe including a body portion, an elongated belt-like flexible substrate, connecting members, a resinous portion, and external contacts formed at the ends of the flexible substrate brought out of liquid. The probe further includes a cantilever whose base end is supported to the body portion, a strain resistive element whose resistance value varies according to the amount of displacement of the cantilever, and interconnects electrically connected with the strain resistive element. A probe tip is formed at the front end of the cantilever. The flexible substrate has an interconnect pattern sandwiched between two insulating sheets. The flexible substrate supports the body portion while the cantilever protrudes outwardly. At least one end of the flexible substrate is brought out of liquid. The connecting members connect the interconnects with the interconnect pattern. The interconnects, connecting members, and the portions of the connecting members electrically connected with the interconnect pattern are coated with the resinous portion.