PURPOSE: To actively introduce out dust or the like to a drainage basin together with rainwater, and prevent the clogging of a gap in pavement having a drainage function by arranging head races at the preset intervals between a drainage layer and a water stopping layer for introducing out the rainwater to the drainage basin.

CONSTITUTION: A water stopping layer 2 is first laid on the upper surface of a subgrade 1 and, then, a drainage layer 3 as pavement having a drainage function and made of a porous asphalt mixture or the like is laid on the upper surface of the layer 2. Also, a head race 10 is formed between the layers 2 and 3. Furthermore, head races 10 for introducing out rainwater to a drainage basin 4 at the side of the layer 3 are arranged on the upper surface of the layer 2 at the prescribed intervals. Also, the head race 10 is provided with a water conductor formed out of a non- permeable material with a projection. In this case, slit drains 5 are provided on the upper surface of the layer 2, and the drains 5 at both right and left sections are provided with drainage basins 4 at the preset intervals, thereby washing away dust or the like externally, together with rainwater, via the water conductor. According to this construction, a gap in pavement with a drainage function can be protected against clogging.