Oscillatory flow in a loop channel consisting of a T-branch, two reservoirs and connecting pipes was experimentally investigated. It was found that the oscillatory flow including a constant circulation flow component is induced in the loop channel by a reciprocating flow given to a branch of the loop channel. Pressure differences between two exits of the T-branch and between inside and outside of the reservoirs cause the constant circulation flow component in the oscillatory flow. We investigated the relationship between the reciprocating flow given to the loop channel and the constant circulation flow component. We also investigated the relationship between the reciprocating flow and the pressure differences at the T-branch and at the reservoirs.