Temperature of space environment was measured with the mechanical thermometer using a bimetallic strip coil for the Tanpopo mission. The Tanpopo mission was a multi-year passive exposure experiment for astrobiology exposure and micrometeoroid capture on board the Exposed Experiment Handrail Attachment Mechanism (ExHAM) at the Japanese Experiment Module ‘Kibo’ (JEM) Exposed Facility (EF) on the International Space Station (ISS). Since its microbial exposure experiment requires recording the maximum temperature that the Tanpopo exposure panel senses, we have developed a mechanical thermometer with no electric power supplied from the ExHAM. At a given time and orbital position of the ISS, the thermometer indicator was video-imaged by the extravehicular video camera attached to the JEM-EF. With these images analyzed, we were able to derive the maximum temperature of the exposure panels on the space pointing face of the ExHAM as 29±5℃. Furthermore, the thermometer endured use more than three years and demonstrated that the durability was particularly superior.