A prefilled syringe of a before-use mixing type not requiring a bypass portion defined by a recessed inner surface portion of an outer cylinder, including first and second gaskets (4,5) fitted in the outer cylinder (2), and non-rotatively and complementarily shaped engagement portions (12, 13) respectively at a front end of the first gasket (4) and a rear end of the second gasket (5) to reduce the period for transferring a liquid between two chambers separated by the gaskets. During storage, the engagement portions abut each other to be kept out of engagement with each other, whereby a drug containing space is defined between the gaskets. When a liquid is transferred from a space defined on a rear side of the first gasket (4) to the drug containing space, the internal pressure of the drug containing space is prevented from being excessively increased.