A drug-filled synthetic resin ampule said synthetic resin ampule includes an ampule main body and a drug stored in said ampule main body ; said ampule main body includes a distal end portion , a hollow portion having a drug storing portion , and an annular breakable portion provided between a lower portion of said distal end portion and an upper portion of said hollow portion ; said ampule main body includes no inner surface protrusion on an inner lateral portion thereof which is located on a side toward said distal end portion with respect to said annular breakable portion ; said distal end portion is configured such that an inner top surface of said distal end portion is located near a plane (S) defined by said annular breakable portion , wherein the inner top surface of said distal end portion is flat; and an inner surface of said distal end portion is a low-drug-retention surface, wherein said distal end portion includes a corner portion of said inner flat top surface being a curved surface having no edge; wherein said inner lateral portion extends from said inner surface of said annular breakable portion to said corner portion of said inner flat top surface , wherein said lateral portion is a hollow portion whose diameter decreases toward said inner flat top surface , said inner surface of said upper portion of said hollow portion has a mouth portion whose diameter increases from said inner surface of said annular breakable portion toward said lower portion of said hollow portion , said low-drug retention surface of said inner surface of said distal end portion is provided by the inner flat top surface , said corner portion of said inner flat top surface and said inner lateral portion . said synthetic resin ampule includes an ampule main body and a drug stored in said ampule main body ; said ampule main body includes a distal end portion , a hollow portion having a drug storing portion , and an annular breakable portion provided between a lower portion of said distal end portion and an upper portion of said hollow portion ; said ampule main body includes no inner surface protrusion on an inner lateral portion thereof which is located on a side toward said distal end portion with respect to said annular breakable portion ; said distal end portion is configured such that an inner top surface of said distal end portion is located near a plane (S) defined by said annular breakable portion , wherein the inner top surface of said distal end portion is flat; and an inner surface of said distal end portion is a low-drug-retention surface, wherein said distal end portion includes a corner portion of said inner flat top surface being a curved surface having no edge; wherein said inner lateral portion extends from said inner surface of said annular breakable portion to said corner portion of said inner flat top surface , wherein said lateral portion is a hollow portion whose diameter decreases toward said inner flat top surface , said inner surface of said upper portion of said hollow portion has a mouth portion whose diameter increases from said inner surface of said annular breakable portion toward said lower portion of said hollow portion , said low-drug retention surface of said inner surface of said distal end portion is provided by the inner flat top surface , said corner portion of said inner flat top surface and said inner lateral portion . <EOS>