An object is to provide a novel temperature measuring catheter capable of planarly grasping a temperature distribution in an inner portion of a hollow organ, such as an esophagus, in a body and capable of reliably measuring the temperature of a region (region whose temperature is raised by ablation) that should be monitored. A catheter of the present invention includes: a catheter shaft (10) having a multi-lumen structure including a fluid-flowing lumen (11) for a fluid； a handle (20) connected to a proximal end side of the catheter shaft (10)； a balloon (30) connected to a distal end side of the catheter shaft (10) and configured to be inflated by the fluid that flows through the fluid-flowing lumen (11), the balloon (30) being flat during inflation； and a plurality of temperature sensors (40) planarly disposed on one surface side of the balloon (30).
