An apparatus for measuring weight of a substance placed within a substrate space which is subjected to sever conditions, including a measuring unit having a transducer and placed within a measuring space, a partition member provided between the measuring space and the substance space and having hole through which said measuring space is communicated with said substance space, a rod-like member extending through said hole formed in the partition member such that a first end of said force transferring member situates within said substance space and a second end of said force transferring member situates within said measuring space, a parallel link mechanism arranged within the measuring space and connected with the rod-like member, a magnetic fluid provided in a space within said hole such that said substance space and measuring space is isolated from each other in a liquid tight manner by means of said magnetic fluid, and a magnetic force generating unit producing a magnetic force such that said magnetic fluid is kept in position by said magnetic force.