To provide a thermosetting resin composition with excellent heat resistance, satisfactory electric characteristics, and remarkably improved brittleness, and a manufacturing method therefor.

A polyfunctional phenol compound, a diamine compound and an aldehyde compound are heated to react each other to obtain the thermosetting resin having dihydro benzoxazine structure expressed by general formula (IV), and a layered silicate is added further thereto, in this manufacturing method for the thermosetting resin composition of the present invention.