PURPOSE: To reduce the size of an infrared sensor which can detect infrared rays at a wide angle.

CONSTITUTION: In a small-sized infrared sensor in which an infrared detecting element 3 is enclosed in a recessed section 7a formed into an enclosing silicon substrate 7 by joining the substrate 7 to an element substrate 1 on which the element 3 is formed, part of the substrate 7 is formed in a lens-like shape. Therefore, the infrared sensor and an infrared-ray condensing optical system can be integrated into one body and the size of the sensor can be reduced. In addition, it becomes unnecessary to consider the assembly of the sensor and optical system and, since no separate optical system is required, the cost of the sensor can be suppressed.