Battery unit mounting structure of electric vehicle

A battery unit mounting structure of an electric vehicle, comprising:

• a floor panel;
• a pair of right-and-left floor frames provided below the floor panel, each of which forms a closed-cross section extending longitudinally cooperatively with the floor panel;
• and
• a battery unit supporting plural battery modules and mounted at the pair of floor frames,
• wherein said battery unit comprises the battery modules and a battery case storing the plural battery modules and attached to said pair of floor frames, and
• mounting rigidity of part of said plural battery modules mounted at said battery case is set to be lower than that of other part of the plural battery modules mounted at the battery case so as to lower a peak of vibration amplitude which is defined as a vibration width, in a vertical direction, of an end portion, in a vehicle width direction, of the plural battery modules in a case where said floor panel vibrates at a frequency of 20-50 Hz and said plural battery modules roll around an axial line which extends in a vehicle longitudinal direction, passing a central point, in the vehicle width direction, of the plural battery modules.