To obtain a washer assembled thin head screw with the basic function of a screw that maintains and assembles the washer capable of adhering to the head seat face to the screw while tightening the screw.

The washer-assembled screw comprises a screw consisting of a head 2 and a leg 4 having a screw thread 3 and a washer 20 held between the head seat face 6 and the screw thread 3. The screw 1 has an annular surface of a large diameter at the top head 5, and the tapered reinforcement section 7 between the sheetface 6 and the screw head 3. The washer 20 has a conical guide hole 21 with a large inner diameter of the contact side to the head seat face 6 and a small diameter of the opposite side. The washer is constituted by assembling the washer to the reinforcement section 7 by setting the large side of inner diameter to the seat face side. Therefore, protrusion quantity of the screw is small, and incongruity is not felt even if it is used for the product of this thickness. On the other hand, sufficient tightening power is obtained without damaging the tightening function, because a sufficient cross hole is obtained. Also, cutting off of the neck part, etc., is hard to occur even if large tightening power is applied.