To provide a working jig which can apply a process such as drilling easily at an accurate position of an FRP product (a bathtub).

This working jig for FRP product is equipped with a main body 11 made of FRP which comes into contact with a surface to be processed (an internal wall surface part (h) on which a recessed part (d) and a jetting hole under the recessed part (d) are provided.), and an engaging part 12 made of FRP which is integrally extended from the main body 11 and engages the main body 11 with an FRP product (a), and on the main body 11 two guide holes 111 for screw hole drilling, and one guide hole 113 for jetting hole drilling, are provided. For the engaging part 12, a part where the width of a box part (c) is narrowest, and parts where the width is slightly wider on both sides of the first part, are integrally formed, and the engaging part 12 cannot move on the box part (c). Therefore, the main body 11 can be joined to the surface to be processed at this location only.