A Signal-to-Noise (SN) ratio maintained scanning-condition recalculating unit re-sets a value of a scanning parameter other than an SN ratio included in scanning conditions when the size of a Field Of View (FOV) to be set for a scan is changed, so as to make the SN ratio of an image to be taken under after-change scanning conditions equal to or larger than the SN ratio of an image assumed to be taken under before-change scanning conditions. A scanning-condition edit/scan positioning unit then sets scanning conditions based on the value of the scanning parameter recalculated by the scanning-condition recalculating unit.