To enhance safety of infusion injection by positively confirming the end of an infusion solution by visual observation of the dripping state of the infusion solution in infusion injection, and automatically closing a lower through-tube port hole 7 with a float valve for safety to prevent the inflow of air therefrom.

This infusion monitoring safety instrument has the float valve 1 inserted in an infusion monitoring cylinder 3. The float valve 1 floating in accordance with the presence of the infusion solution floats according to the quantity of the infusion solution when there is the infusion solution and goes up and down in the state of the float valve 2, but when the infusion solution decreases and the drip of the infusion solution stops, the float valve 1 is sucked to the through-tube port hole 7 with the progress of infusion injection of the infusion solution from the monitoring cylinder, and comes in close contact with the through-tube port hole 7 to automatically prevent the inflow of air.