PURPOSE: To improve the locking strength and reliability on a composite panel for building, such as earthenware plate tiles, having a backup layer formed on a back.

CONSTITUTION: A plurality of recessed grooves 3...3 in a shape in cross section where a diameter is increased at a deep part are formed in a back 2, a backup layer 5 formed of fiber-reinforced cement is formed in the back of the tile 4 in length ranging not throughout the whole surface in the direction of width B or height L, and the recessed grooves 3...3 are filled deep to the interior with a fiber-reinforced cement material for integral lamination. Further, oblong holes 7...7 the bottoms 7A of which reach the interior of the respective recessed grooves 3...3 and which have length shorter than those of the recessed grooves 3...3 are formed in a back 6 of the layer 5 along the respective recessed grooves 3...3.