A mobile body capable of improving the accuracy of collision judgment. The mobile body including a fuel cell system has a first sensor which detects a physical quantity concerning the moving state of the mobile body, a second sensor which detects a physical quantity concerning the operation state of the fuel cell system, and a judgment section which receives detection signals from the first and second sensors to judge the presence of the collision of the mobile body based on the two detection signals. The judgment section can change a threshold value to be compared with the detected value of the first sensor in accordance with the detected value of the second sensor, to judge the presence of the collision of the mobile body. The first sensor can be constituted of an acceleration sensor, and the second sensor can be constituted of a gas pressure sensor or the like.