A numerical study on the premixed wrinkled flame front has been conducted in order to examine the motion of the wrinkled flame front and flame/flow interaction in an oscillating flow field. The conventional G-equation is solved to determine the time dependent behavior of the flame front by using a model in which the flame front is regarded as a source of volume and vorticity. To confirm the numerical simulation, the response of the wrinkled premixed flame under the oscillating flow field is experimentally observed. The experimental results, where flame/flow interaction is clearly observed, can be depicted by the numerical analysis. The wrinkled region of the flame front hardly responds to the upstream flow oscillation even if this oscillation is as large as the mean velocity of the flow field. The behavior of the wrinkled flame front is found to result from flame/flow interaction due to volume expansion and vorticity production at the flame front. Especially in a time varying flow field, vorticity production plays a decisive role in the motion of the wrinkled region of the flame front by counteracting the oscillating flow field.