ably made of a high thermal conductivity metal such as copper, aluminum, or zinc. [0040] The sensor housing 110 is airtightly attached to the speculum 100, and therefore, moisture cannot intrude into between them. [0041] A first step 130 is formed around the leading end portion of the sensor housing 110, and an airtight member 140 is attached onto the first step 130 by using an epoxy resin, so tha