Abstract: An infrared radiation detector so adapted as to prevent the image signals from deteriorating due to the short length of leads extending within the cryogenic container with the infrared radiation sensing element accommodated within and to correspond to the increasing number of the leads and terminals, associated with a high density of elements. The infrared radiation detector is composed of an inner cylinder and an outer cylinder. The outer cylinder is disposed so as to lie in the same plane as the sub-package on which the multi-layered ceramic lead plate composed of a plurality of bonding pads for wire bonding, internally embedded lead layers, and plug-in terminals for fetching signals is mounted. The bonding pad of the sub-package is bonded to the bonding pad of the ceramic lead plate through a wire bonding.