The effect of periodic operation on the mixing process of a non-element mixer was investigated experimentally. Into the main flow of glycerin in a pipe of 10 mm ID, more glycerin was injected periodically through a perpendicular branch pipe of 3 mm ID. The flow was intrinsically laminar. When the branch flow was injected, the fluid was folded and stretched under the influence of the parabolic velocity distribution of the pipe flow. The flow pattern was determined by the flow volumes of the main and branch flows in one period. The mixing pattern was modeled as an axi-symmetric interface. The progress of the mixing was estimated by advective mixing and mixing due to molecular mixing. The advective mixing was quantitatively estimated from the increase in the area of the interface between the main flow and the branching flow. The mixing due to molecular mixing was estimated from the concentration distribution in the pipe. In addition, the ratio between the area where advective mixing is dominant and that where mixing due to molecular diffusion is dominant was defined. The progress of the mixing could be estimated from the total value of the advective mixing and the mixing due to molecular diffusion and the area ratio between advective mixing and mixing due to molecular diffusion.