An injection device (1) for powdered drugs comprises: a cylindrical guide member (21) mounted to a container body (11); a gas generating agent (43) that is accommodated in a cylindrical section (26); a cylindrical breaking member (31) that drops the gas generating agent (43) into water in the container body (11) by breaking a sealing portion (41); a piston (63) that slides against a bottom sliding inner circumferential wall (53) in an airtight manner and that defines a gap with an upper enlarged diameter inner circumferential wall (55); and a powdered drug (30) that is accommodated on the piston (63).