PURPOSE: To prevent rainwater that enters from between flat roof tiles from leaking to a roof bed by covering the roof bed with roof tile beds each provided with a first and second independent drip grooves, while arranging the roof tile beds in rows with their vertical positions displaced right and left alternately.

CONSTITUTION: A roof bed is covered with roof tile beds S1 each having a first 16 and second 17 independent drip grooves therein, while the roof tile beds are arranged in rows with their vertical positions displaced right and left alternately. Should rainwater enter from the butt portions of right and left flat root tiles in a rainstorm, etc., the rainwater flowing into the third drip grooves 8... the upper roof tile beds S1 is drawn off from the second drip grooves 17 of the lower roof tile beds into other third drip grooves 8 starting from the second drip grooves 17. Rainwater flowing into the first drip groove 16 of the upper roof tile beds S1 from the butt portions of the right and left flat roof tiles is drawn off by flowing into the second drip grooves 17 of the lower roof tile beds S1. It is thus made possible to prevent rainwater from overflowing the first drip groove 16 and leaking to the roof bed comprising sheathing roof boards.