An expandable polyurethane composition contains (A) a polyisocyanate, (B) an active hydrogen containing compound containing (B1) a polyol and (B2) water, and (C) a cross-linking agent composition. The cross-linking agent composition (C) contains a cross-linking agent (C1) and a carboxylic acid (C2). The cross-linking agent (C1) can be selected from an alkanolamine (a) represented by an expression: HxR1yN((R2O)nH)3-x-y, and an aminosilane (b) represented by an expression: (R3O)qR43-qSi—R5—(NHCH2CH2)pNR6R7. A content of the cross-linking agent composition (C) is 0.1 parts by mass to 20 parts by mass relative to 100 parts by mass of the active hydrogen containing compound (B), and the containing number of moles of the cross-linking agent (C1) is larger than that of the carboxylic acid (C2). It is possible to delay a reaction without deteriorating a final reactivity, to suppress viscosity increasing just after an injection into a mold, to improve hardness and to attain lowering of a pressure to be applied to a cell communication.