We observed the unidentified TeV gamma-ray source HESS J1804 - 216 with the CANGAROO-III atmospheric Cerenkov telescopes from May to July in 2006 .
We detected very high energy gamma rays above 600 GeV at the 10 \sigma level in an effective exposure of 76 hr .
We obtained a differential flux of ( 5.0 \pm 1.5 _ { stat } \pm 1.6 _ { sys } ) \times 10 ^ { -12 } ( E/1 TeV ) ^ { - \alpha } cm ^ { -2 } s ^ { -1 } TeV ^ { -1 } with a photon index \alpha of 2.69 \pm 0.30 _ { stat } \pm 0.34 _ { sys } , which is consistent with that of the H.E.S.S .
observation in 2004 .
We also confirm the extended morphology of the source .
By combining our result with multi-wavelength observations , we discuss the possible counterparts of HESS J1804 - 216 and the radiation mechanism based on leptonic and hadronic processes for a supernova remnant and a pulsar wind nebula .