A stereoscopic endoscopic image processing apparatus includes: a synchronization adjustment portion that performs a synchronization adjustment between a left-eye image signal and a right-eye image signal; an image analysis portion that analyzes a region that an image of a treatment instrument occupies in a peripheral region around a central region in an image of one image signal; a blur region setting portion that, with respect to the image in the peripheral region around the central region in which blur processing is not performed, sets a region in which to perform blur processing in accordance with an analysis result of the image analysis portion; and an image compositing portion that composites and outputs a 3D image with respect to which blur processing is performed on the left-eye image and the right-eye image, respectively, in accordance with a setting result of the blur region setting portion.