1. A magnetic resonance imaging system for performing an imaging scan based on a desired pulse sequence in order to obtain an MR image at a desired region of an object to be imaged, the system comprising: a preparation scan performing unit configured to perform a preparation scan to acquire data for a plurality of preparatory images at the desired region of the object, the preparation scan being performed with an amount of a desired parameter of the pulse sequence changed every preparatory image; a preparatory image producing unit configured to produce the plurality of preparatory images from the data acquired by the performance of the preparation scan; a displaying unit configured to display the plurality of preparatory images; a selection unit configured to allow a desired preparatory image to be selected from the plurality of preparatory images displayed; and a setting unit configured to set, into the imaging scan, the amount of the desired parameter given from the selected preparatory image.