The device for diagnosing tissue injury of the invention has a catheter insertable into the body and a radical sensor provided in the catheter, and is characterized in that the radical sensor has a sensor electrode capable of measuring superoxide anion radicals provided at a tip end of the catheter, a lead wire connector for a sensor provided at a basal portion of the catheter, and a lead wire for a sensor for connecting the sensor electrode portion to the lead wire connector for a sensor. With the device, in vivo free radicals typified by superoxide anions in systemic organ or tissue injury caused by cerebral ischemia reperfusion injury, severe infection or sepsis can be promptly and quantitatively monitored, and whether the in vivo tissue conditions are good or not can be accurately diagnosed.
