A flow rate control device is provided in which a control base (5) is provided with a first joining flange (35), made of a synthetic resin, extending in a direction perpendicular to an axial direction of a mounting hole (19), a stator (20a) of an actuator (20) is provided with a second joining flange (36), made of a synthetic resin, opposing the first joining flange (35), a welding concave portion (39) is provided in one of opposing faces of the first and second joining flanges (35, 36), a welding convex portion (40) that is to be inserted into the welding concave portion (39) is provided on the other of the opposing faces, a heating element (44) for welding a bottom part of the welding concave portion (39) and a periphery of an extremity part of the welding convex portion (40) is disposed between the bottom part and the extremity part, and the first and second joining flanges (35, 36) are provided with welding restriction parts (45, 46) that maintain a defined value by abutting against each other when the am