A vacuum circuit breaker (VB) comprising: - a main circuit structure body including a vacuum switch having a fixed contact and a movable contact, a fixed side terminal connected to the fixed contact of the vacuum switch , a movable side terminal connected to the movable contact of the vacuum switch , and an insulation rod coupled to the movable contact of the vacuum switch , the insulation rod opening and closing the fixed contact and the movable contact; and - an insulating holder for supporting the main circuit structure body, - wherein the insulating holder is a frame structure body having opening portions in top and bottom surfaces and both side surfaces of a section in which the vacuum switch is disposed and a section in which the insulation rod is disposed, - the frame structure body includes two U-shaped frames stacked, insulating holder fixation portions integrally and vertically connecting one ends of the two stacked U-shaped frames close to the opening portions of the frame structure body, and intermediate frames coupling intermediate portions of the U-shaped frames , and - wherein the frame structure body includes one end of an upper frame , which is the upper one of the U-shaped frames , and one end of a lower frame , which is the lower one of the U-shaped frames , on the opening side , are integrally coupled by the insulating holder fixation portion extending vertically, and the intermediate portions of the U-shaped upper frame and lower frame are coupled integrally by the intermediate frames extending vertically, - the insulation rod is disposed in a space surrounded by the insulating holder fixation portions , the intermediate frames , and parts of the U-shaped frames close to the insulating holder fixation portions , and - the vacuum switch is disposed in a space surrounded by corners of the U-shaped frames and the intermediate frames . - a main circuit structure body including a vacuum switch having a fixed contact and a movable contact, a fixed side terminal connected to the fixed contact of the vacuum switch , a movable side terminal connected to the movable contact of the vacuum switch , and an insulation rod coupled to the movable contact of the vacuum switch , the insulation rod opening and closing the fixed contact and the movable contact; and - an insulating holder for supporting the main circuit structure body, - wherein the insulating holder is a frame structure body having opening portions in top and bottom surfaces and both side surfaces of a section in which the vacuum switch is disposed and a section in which the insulation rod is disposed, - the frame structure body includes two U-shaped frames stacked, insulating holder fixation portions integrally and vertically connecting one ends of the two stacked U-shaped frames close to the opening portions of the frame structure body, and intermediate frames coupling intermediate portions of the U-shaped frames , and - wherein the frame structure body includes one end of an upper frame , which is the upper one of the U-shaped frames , and one end of a lower frame , which is the lower one of the U-shaped frames , on the opening side , are integrally coupled by the insulating holder fixation portion extending vertically, and the intermediate portions of the U-shaped upper frame and lower frame are coupled integrally by the intermediate frames extending vertically, - the insulation rod is disposed in a space surrounded by the insulating holder fixation portions , the intermediate frames , and parts of the U-shaped frames close to the insulating holder fixation portions , and - the vacuum switch is disposed in a space surrounded by corners of the U-shaped frames and the intermediate frames . <EOS>