A first body is bonded with a second body to accommodate a sensor element therein. An annular convexity is formed at either the first body or the second body along with its peripheral end border. On the other of the first body and the second body, an annular concavity is formed to engage with the convexity. The convexity engages with the concavity to form an inner gap and an outer gap. Glue is filled in the inner gap and the outer gap. The peripheral surface of the convexity and the peripheral surface of the concavity, where the glue is bonded, have plural protrusions.