A screw block installation structure for a junction box in which a screw block is installed to a screw block attaching portion having a screw block housing space in a component attachment block in a junction box, the component attachment block is housed together with the screw block inside a frame, and a connecting member is screw-connected to a screw member of the screw block, the screw member having a vertical axis of the screw block, wherein a lateral side opening is disposed in the screw block attaching portion, and the screw block is laterally installed to the screw block housing space through the side opening is provided.