A method for manufacturing a flow sensor having: a first chip mounting section; and a first semiconductor chip arranged on the first chip mounting section, the first semiconductor chip having: a flow detecting unit formed on a main surface of the first semiconductor chip; and a diaphragm formed by thinning the first semiconductor chip in a region of a rear surface opposite to the main surface of the first semiconductor chip so as to face the flow detecting unit, and a part of the first semiconductor chip being sealed by a sealing body containing a resin in a state in which the flow detecting unit formed in the first semiconductor chip is exposed, the method comprising the steps of: (a) preparing a base material having the first chip mounting section; (b) preparing the first semiconductor chip; (c) mounting the first semiconductor chip on the first chip mounting section; and (d) after step (c), sealing a part of the first semiconductor chip by the sealing body while leaving the flow detecting unit formed in the first semiconductor chip exposed, wherein step (d) includes the steps of: preparing an upper mold and a lower mold; after step, sandwiching the base material having the first semiconductor chip mounted thereon by the upper mold and the lower mold through a second space, while pressing a part of the upper mold against an upper surface of the first semiconductor chip and forming a first space surrounding the flow detecting unit between the upper mold and the first semiconductor chip; after step, casting the resin into the second space; after step, forming the sealing body by hardening the resin; and after step, releasing the sealing body from the lower mold, characterised in that, in step, the sealing body is released from the lower mold by thrusting up, from the lower mold, an ejection pin (EJPN) which is inserted in the lower mold in an outer region outside the first semiconductor chip so as not to overlap with the first semiconductor chip when seen in a direction perpendicular to the main surface of the first semiconductor chip. a first chip mounting section; and a first semiconductor chip arranged on the first chip mounting section, the first semiconductor chip having: a flow detecting unit formed on a main surface of the first semiconductor chip; and a diaphragm formed by thinning the first semiconductor chip in a region of a rear surface opposite to the main surface of the first semiconductor chip so as to face the flow detecting unit, and a flow detecting unit formed on a main surface of the first semiconductor chip; and a diaphragm formed by thinning the first semiconductor chip in a region of a rear surface opposite to the main surface of the first semiconductor chip so as to face the flow detecting unit, and a part of the first semiconductor chip being sealed by a sealing body containing a resin in a state in which the flow detecting unit formed in the first semiconductor chip is exposed, the method comprising the steps of: (a) preparing a base material having the first chip mounting section; (b) preparing the first semiconductor chip; (c) mounting the first semiconductor chip on the first chip mounting section; and (d) after step (c), sealing a part of the first semiconductor chip by the sealing body while leaving the flow detecting unit formed in the first semiconductor chip exposed, (a) preparing a base material having the first chip mounting section; (b) preparing the first semiconductor chip; (c) mounting the first semiconductor chip on the first chip mounting section; and (d) after step (c), sealing a part of the first semiconductor chip by the sealing body while leaving the flow detecting unit formed in the first semiconductor chip exposed, wherein step (d) includes the steps of: preparing an upper mold and a lower mold; after step, sandwiching the base material having the first semiconductor chip mounted thereon by the upper mold and the lower mold through a second space, while pressing a part of the upper mold against an upper surface of the first semiconductor chip and forming a first space surrounding the flow detecting unit between the upper mold and the first semiconductor chip; after step, casting the resin into the second space; after step, forming the sealing body by hardening the resin; and after step, releasing the sealing body from the lower mold, preparing an upper mold and a lower mold; after step, sandwiching the base material having the first semiconductor chip mounted thereon by the upper mold and the lower mold through a second space, while pressing a part of the upper mold against an upper surface of the first semiconductor chip and forming a first space surrounding the flow detecting unit between the upper mold and the first semiconductor chip; after step, casting the resin into the second space; after step, forming the sealing body by hardening the resin; and after step, releasing the sealing body from the lower mold, characterised in that, in step, the sealing body is released from the lower mold by thrusting up, from the lower mold, an ejection pin (EJPN) which is inserted in the lower mold in an outer region outside the first semiconductor chip so as not to overlap with the first semiconductor chip when seen in a direction perpendicular to the main surface of the first semiconductor chip.