To realize an image diagnostic device and an endoscope system by which the difference between a normal part and a lesion part in an examinee can be quantitatively judged, and which displays easily observable endoscope image for enabling to do the same diagnosis regardless of the degree of observer's skillfulness.

A IHb is calculated every pixel from the endoscope image inputted by an inter-image arithmetic part 92. The calculated IHb is compared with a prescribed range by an arithmetic comparison part 93. A color slurring quantity for one frame is calculated from the endoscope image inputted by a color slurring quantity calculating part 94. The color slurring quantity is compared with a prescribed value by a color slurring quantity comparison part 95, and the endoscope image inputted by a delay 96 is converted by an image converting part 97 based on the comparison result, and is outputted as a composite image. The image converting part 97 executes image conversion in the region in which the IHb is judged to be abnormal regarding the frame in which the color slurring quantity is judged to be small. On the other hand, it does not convert the frame having a large color slurring quantity or the region in which the IHb is judged to be normal.