A visualization study was carried out to investigate the effects of phase difference qualitatively by examining wake pattern on the phase difference of a dragonfly type wing model. The model was built with scaled-up, flapping wings composed of a paired wing with fore- and hind-wings in tandem that mimick the wing form of a dragonfly. The present study was conducted by using the smoke-wire technique and an electronic device below the tandem wings was mounted to find the exact wing position angles. Uncertainties in wing position angle are about $pm$$1.0^{cire}$ and instantaneous wing positional angle varies from $-16.5^{cire}$ to $+22.8^{cire}$. The tests were made at phase differences between the fore-wing and hind-wing at $0^{cire}$, $90^{cire}$, $180^{cire}$ and $270^{cire}$. The results show that Karman vortex structures were produced at phase differences of $90^{cire}$, $180^{cire}$ and $270^{cire}$, but Karman vortex structures were not observed at the phase difference of $0^{cire}$.