A flame-retardant epoxy resin composition wherein (A) epoxy resin, (B) a curing agent and (C) a phosphorous-containing compound expressed by the following general formula (1) are contained; a prepreg using the same and a laminated plate using said prepreg; wherein m expresses an integer from 2 to 10, R1 and R2 each independently express an alkyl group or an aryl group, R3 expresses a hydrocarbon group that may contain an oxygen atom, a sulfur atom or a nitrogen atom, X expresses an oxygen atom or a sulfur atom, Y expresses an oxygen atom, a sulfur atom or —NR4—, and in this regard, R4 expresses a hydrogen atom, an alkyl group or an aryl group.