A drug-filled synthetic resin ampule (1a, 1k) said synthetic resin ampule (1a, 1k) 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 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 (1a, 1k) 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 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.