An infrared apparatus includes a case, and an infrared device to input and/or output infrared rays. In the infrared apparatus in which the infrared device is received in the case, the case has an infrared transmitting window part which transmits only infrared light and which does not transmit visible light. Of a light transmitting resin through which near-infrared laser used for near-infrared laser welding passes and a light absorbing resin which emits heat and melts when receiving the near-infrared laser, the infrared transmitting window part is made of the light transmitting resin.