The UBVIKC CCD photometry was performed in the central region(~ 20' × 20') of the extremely young open cluster IC1805. Member stars were selected in the (B-V)-(U-B) and (V-I)-(B-V) color-color planes. Applying recent stellar evolutionary models, we derived the age, age-spread, and initial mass function(IMF) of the cluster. IC1805 was found to be an extremely young(tage ~ 1.5Myr) and has a flat IMF with the slope of Γ=-1.0±0.2.