To provide an insert molding die which can successfully slide without the generation of a draggging K by a locking block to a sliding core and dipenses with maintenance services.

The insert molding die is equipped with a sliding promotion mechanism 30 for promoting the sliding of the locking block 18 between guide plates 19 and the locking block 18. The sliding promotion mechanism 30 is composed of a plurality of rollers 31 installed rotatably on a contact surface with the guide plates 19 in the locking block 18. The rollers 31 are of a slender bar form and installed, at a specified interval, on a base 32 through a support part 33. Besides, the rollers 31 are freely rotatable centering around the support part 33. In addition, in the locking block 18, the rollers 31 are installed by brazing the base 32 to the upper part and the lower part of the contact surface with one of the guide plates 19.