To obtain an infrared detector in which the electromagnetic shielding effect of a metal case is made sure by a method wherein a protrusion is formed near a window at the metal case so as to pierce an optical filter, the tip part of the protrusion is coupled to the window at the metal case in a state that it is pierced through the part of an insulating film at the optical filter and, the optical filter is fixed and bonded to the window at the metal case by using a jointing material.

A window 21 and burrs 22, 23 are formed at the upper part of a cap 2 by a press working operation, and an optical filter 4 is installed. A base 1 and the cap 2 are airtightly sealed by a welding operation or the like. The optical filter 4 is pierced through the burrs 22, 23 as protrusions at the cap 2 so as to be mounted, and the circumference of the optical filter 4 is coated with a jointing material 14 so as to be hardened and bonded. Thereby, tip parts of the burrs 22, 23 are pierced through insulating films 42 at the optical filter 4 so as to come into contact with a semiconductor substrate 41, and the cap 2 and the optical filter 4 are electrically connected surely.