There are provided a synthetic resin joined body and a method of manufacturing the same, with which it is possible to secure both of sealing performance of a fluid passage and joint strength between synthetic resin parts, even if an area of a portion to be welded is reduced.
The synthetic resin joined body includes: a baffle plate 110; an oil passage forming member 120 which comes in contact with the baffle plate 110; an oil passage 130 which is formed between the baffle plate 110 and the oil passage forming member 120 and through which lubricant flows; a sealing portion 140 which is formed by welding the baffle plate 110 and the oil passage forming member 120 to each other on an outer side of the oil passage 130 to seal a periphery of the oil passage 130; and a joint portion 150 for joining the baffle plate 110 and the oil passage forming member 120 to each other.