Provided is a medical image diagnosis apparatus which requires a small area for installation, has a short length in an axial direction of the apparatus, can reduce a problem of the strength of a top plate, and can simultaneously carry out dynamic PET-imaging of the entire body. A top plate (61) on which an examinee lies is moved through a tunnel of a CT gantry (2) and a PET gantry (3) to execute CT imaging and PET imaging. A PET unit consisting of a plurality (e.g. seven) of PET units (32) has a length of 2 m in the axis direction, the visual field thereof covers the whole body and the whole body can be simultaneously subjected to dynamic PET-imaging. For the maintenance of the PET gantry (3), the diagnosis apparatus is separated at an arbitrary PET unit (32) to be maintained, the apparatus slides on a rail (31) in the axis direction and is separated for maintenance operation. Accordingly, a large space for maintenance is not required and the area for installation is small.
