This paper describes results and analysis of experiment of compression behavior parallel to grain of glulam (Norway Spruce, Japanese cedar, and Japanese cypress), especially in damage zones near loading plates and joints. To investigate the influence factors of physical properties and the mechanism of the damage zone near the loading plates or the joints, compression tests on 90 specimens and surface-measurement tests on 48 specimens were performed. As a result, it was observed that damage zones existed near the loading plates and the joints. The lengths of the damage zone of wood–wood joints are larger than that of wood–steel joints. The length of the damage zone was independent of the load and the height of the specimens. However, the length of the damage zone and its scatter increase as the width of the cross-section increases, as does the roughness on the contact surface. It was considered that the cause of the damage zone is the roughness on the contact surface and the length of the damage zone depends on the roughness on the contact surface. Therefore, the length of the damage zone depends on the processing accuracy on the contact surface and has an increasing trend as the contact-surface area increases. There was the size effect of the height of the specimens on the compressive strength because of knots.