Phosphorus-containing epoxy resin, epoxy resin composition, prepreg, laminated plate, material for circuit board and cured product

An epoxy resin composition which contains a phosphorus-containing epoxy resin and a curing agent and has a phosphorus content of within a range of 1.0 to 1.8 mass %, wherein the phosphorus-containing epoxy resin is a product obtained from a novolac epoxy resin having a ratio (L/H) of the content (area %, L) of trinuclear bodies to the content (area %, H) of hepta or higher nuclear bodies measured by gel permeation chromatography of within a range of 0.6 to 4.0, and having an average number of functional groups (Mn/E) obtained by dividing a number average molecular weight (Mn) based on a standard polystyrene conversion value by an epoxy equivalent (E) of within a range of 3.8 to 4.8, and a phosphorus compound represented by the following general formula (1) and/or general formula (2):

• in the formulas, R1 and R2 are a hydrocarbon group having 1 to 20 carbon atoms which may have heteroatoms, and may be different from each other or may be the same, and may be linear, branched, or cyclic, or R1 and R2 may be bonded to form a cyclic structure site;
• n1 and n2 each independently represent 0 or 1;
• and A represents a trivalent aromatic hydrocarbon group having 6 to 20 carbon atoms.