A door unit for selectively opening and closing an opening in an object includes a door having a bendable slatted door body and a flexible sheet member positioned over the door body. Guide grooves in the object slidably guide at least the door body, and the respective ends of the door body and the sheet member are connected on one end in the sliding direction. By setting an appropriate spacing between the guide grooves, the generation of noise that would otherwise be caused by the door body and the sheet member rubbing against each other when they are opened or closed, is avoided. The use of the separate sheet member also significantly increases the options for the material to be employed for the design surface of the door unit.