In order to provide an X-ray CT apparatus and the like that reconstruct an image using an iterative approximation method which ensures stable convergence and can be executed at high speed, a computation device 5 of an X-ray CT apparatus 1 calculates matrices A, B, D, R, and R\u2032 on the basis of the scanning conditions input through an input device 6. In the semiconductor device, a node which holds data that is rewritten by arithmetic processing as appropriate and a node in which the data is stored are electrically connected through a source and a drain of a transistor whose channel is formed in an oxide semiconductor layer. Operations, such as calculations, are performed in accordance with different rules that are associated with varying state laws and rules that may vary with insurance account. Overheat prevention device includes a temperature sensing and fusing bar extending to a predetermined length to reach a position around the filter net and has a temperature sensor to detect an internal temperature of the housing, and a thermal fuse to cut off electricity supplied to the heater, when the interior of the housing overheats.