In order to examine the effect of a converging-diverging flow for surfactant solutions in undulating slit channel, the measurement of pressure loss and light scattering were performed. The mixtures of CTAB and NaSal in distilled water were used as test fluids. In the measurement of pressure loss, it is found that the pressure loss in undulating channel becomes larger than that for the straight channel with a same width as undulating one. The excess pressure loss due to an effect of elongational flow occurs at about 1.0 s^<-1> of an apparent stretch rate and depends on the channel geometry. Furthermore, it is confirmed that the scattering pattern at the converging part was different from that at diverging one. These facts suggest that the micellar network structure is significantly affected by the stretch deformation.