To obtain the subject composition capable of shortening a curing time in molding without reducing characteristics of the cured product such as strength and the like by bringing the composition to contain a phenol novolak resin, hexamethylene tetramine and aspecific compound.

This thermosetting resin composition is obtained by comprising 100 pts.wt. of (A) a phenol novolak resin, 7-30 pts.wt. of hexamethylenetetramine and 0.5-30 pts.wt. of (C) a compound expressed by the formula (R1 to R4 are each H, a monovalent alkyl, a monovalent aryl or an alkoxy; R5 is a monovalent alkyl or aryl) and having one 3,4-dihydro-2H-1,3-benzooxazine structure in the molecule. As the ingredient A, a random novolak obtained by reacting (i) a phenol with (ii) a formaldehyde in 0.4-0.95 molar ratio (ingredients ii/i) in the presence of (iii) an acidic catalyst having 0.65-0.9 ortho/para ratio and ≤10 wt.% amount free phenol is preferable.