An in-cylinder pressure detection device which is capable of ensuring stable detection accuracy irrespective of tightening torque applied in mounting the in-cylinder pressure detection device and thermal expansion of component parts of the same. A housing 21 has a top wall 22a and a bottom wall 22b opposed to each other, and is screwed into the body of an internal combustion engine. An inner member 24 extends through the housing 21 such that one end thereof projects into a cylinder C, and has a flange part 24b accommodated in the housing 21. A first piezoelectric element 11c is accommodated in the housing 21 and sandwiched between the bottom wall 22b and the flange part 24b in a preloaded state, for outputting a first detection signal q1 according to the in-cylinder pressure transmitted via the inner member 24. A second piezoelectric element 12c is accommodated in the housing 21 and sandwiched between the top wall 22a and the flange part 24b in a preloaded state, for outputting a second detection signal q2 according to the in-cylinder pressure transmitted via the inner member 24.