The present invention provides an image data processing device useful for reducing a burden on patients and the inconvenience of operators when trasncranial magnetic stimulation therapy is carried out, and a transcranial magnetic stimulation apparatus using the image data processing device. An image data processing device is provided with: a storage means for storing a previously captured three-dimensional MRI image of a subject head a three-dimensional external appearance image generation means for generating a three-dimensional external appearance image of the subject head an image generation means for aligning the three-dimensional MRI image and the three-dimensional external appearance image to generate a subject head three-dimensional image obtained by the alignment an after-movement image generation means for, when the subject head has moved, generating a subject head three-dimensional image obtained by alignment after the movement an operation object image generation means for generating an operation object image indicating the current position of an operation object to be moved and operated so as to maintain a positional relationship with a specific portion on the subject head three-dimensional MRI image and a display means for displaying the subject head three-dimensional image after the movement and the operation object image in the same image.Cette invention concerne un dispositif de traitement de données dimages utile pour réduire les contraintes pour les patients et les inconvénients pour les opérateurs quand une thérapie par stimulation magnétique transcrânienne est mise en œuvre, et un appareil de stimulation magnétique transcrânien utilisant ledit dispositif de traitement de données dimages. Le dispositif de traitement de données dimages selon linvention comprend : un moyen de stockage pour stocker une image IRM tridimensionnelle préalablement capturée de la tête dun sujet un moyen de génération dune image daspect externe tridimensionnelle pour géné
