The present invention provides a pancreatic islet isolation method comprising the steps of injecting a protection solution containing a protease inhibitor into the pancreatic duct of an procured pancreas; digesting the pancreas into which the protection solution has been injected; and purifying the digested pancreatic tissue using a purification solution containing a density gradient reagent. A maximum allowable power of the protection unit is less than a power when the driving voltage of the LED is directly applied to the protection unit. The circuit unit is disposed in the circuit receiving space.