A laser light is linearly delivered onto the sample 4. The ions generated from the irradiated area are collected, mass-separated in the mass separator 27, and detected by the detector 28. A mass analysis is repeated while moving the sample stage 3 by a predetermined step width in the x-axis direction so that the one-dimensional mass spectrum information of the sample 4 at a certain rotational position is obtained. Additionally, while the sample 4 is rotated by a predetermined angle, the same measurement is repeated for the entire perimeter, so that the one-dimensional mass spectrum information at each rotational position is obtained. Based on the data obtained in this manner, a reconstruction computational processing is performed by the CT method to reconstruct the two-dimensional distribution image for a substance having a certain mass for example and the image is displayed on the display 35.