An endoscope includes an insertion portion that includes a distal end portion and a bending portion configured to change a direction of the distal end portion. The distal end portion includes a casing having a round shape in a cross-section, and an image pickup module that includes an optical module section including a plurality of optical members and an image pickup section, the image pickup module having a rectangular shape in a cross-section, and the image pickup section includes an image pickup device and a semiconductor stack in which a plurality of semiconductor devices is stacked, and entirety of the image pickup module is completely housed inside the casing.