To provide a low cost infusion solution residual amount monitoring apparatus having a simple structure.

A transparent or translucent storage box 11 jointly provided with a retainer 40 detachably assembled with an infusion stand S is provided with a hook part 13a vertically penetrating the storage box 11 and having its upper end part connected to the tip part of a balance rod 13 supported by a horizontal support shaft 12 into a balance; an infusion bag B hung on the hook part 13a; a detecting switch 14 operated by abutment of an abutment device 13c fixed and disposed with an insulator to the balance rod 13 lowered when the residual amount of the infusion solution in the infusion bag B reaches a prescribed amount; and a device body 10 notifying that the residual amount of the infusion solution is a little, by an alarming by a sound device 15 provided in the storage box 11, lighting of a light emission lamp 16, or both of them by the operation of the detecting switch 14.