1. A medical image display device comprising, a region of interest setter for setting a first region of interest being a region of an observation site in volume data, and a second region of interest being a lesion candidate region relating to the observation site, a display image generator for generating a display image that allows a size of an adjacent region of interest, adjacent to the first region of interest on a projection line of interest, to be distinguishable, when a pixel having a reference pixel value on the projection line of interest corresponds to a pixel of the first region of interest and the adjacent region of interest is the second region, and a display unit for displaying the display image, wherein when the pixel having the reference pixel value on the projection line of interest corresponds to the pixel of the first region of interest, the display image generator determines a weight coefficient according to the size of the adjacent region of interest, and sets a value as a projected pixel value for the projection line of interest, the value being weighted the weight coefficient to a pixel value based on a group of pixels in the adjacent region of interest and the reference pixel value on the projection line of interest.