A discharge tube 10 includes first electrode 12, second electrode 14 and third electrode 16 which are arranged in parallel, airtight outer enclosure 22 including first tubular body 18 sandwiched between first electrode 12 and second electrode 14, and second tubular body 20 sandwiched between second electrode 14 and third electrode 16. Through-holes 24 is formed in second electrode 14 and allows internal spaces of first tubular body 18 and second tubular body 20 to communicate with each other. On first electrode 12 and third electrode 16, discharge electrode portions 26 are formed which protrude toward a center of airtight outer enclosure 22 and are disposed opposite to each other with discharge gap 28 provided in between, and discharge gas is filled in airtight outer enclosure 22. The discharge electrode portions 26 are inserted and arranged in through-hole 24 of second electrode 14.