In an assembly method for an endoscope image pickup unit, the endoscope image pickup unit includes a distal end portion main body portion including a front opening portion, a side opening portion, a rear opening portion and an arrangement space portion, a lens section including a distal end lens having an outer diameter that generally fits in the front opening portion, and an image pickup section that fits in the rear opening portion and includes an image pickup device arranged in an image forming position by a lens system such as the lens section. The assembly method includes steps for inserting the lens section into the arrangement space portion from the side opening portion, fitting the inserted lens section in the front opening portion, and fitting the image pickup section in the rear opening portion from a rear of the rear opening portion.
