PURPOSE: To obtain an image with an even resolution, by making the weight of evaluation with respect to a radiation path to an object to be inspected zero outside the data collecting section and larger inside to generate tomographic image by a sequential approximation method.

CONSTITUTION: Receiving a command signal from a control console 54, a CPU51 operates according to a predetermined program to feed a command signal to a mechanism control section 52 and a radiation control section 53 and on the contrary, to receive a status signal for scanning with the console 54 as interface. The CPU51 also receives and memorizes data from a data collecting section 37 and reads out data from own disc memory table at each pixel to be sent to an image reconstruction processing circuit 55, where an image reconstruction processing is done by a sequential approximation method. In this sequential approximation method, a weighting coefficient is applied according to the reliability of the data depending on a radiation path or the like. The weighting coefficient is made zero with respect to the path involved in the collection of no data while a wide range weighting coefficient is used for the data collection section, thereby producing an image with an even resolution.