We have started the photometric observations of SN 2010dn. SN 2010dn was discovered of 17.5 mag in NGC 3184 on May 31.5 by K. Itagaki (CBET 2299). The photometric points seem to be increased as a supernova in the pre-maximum light. Alternatively, in CBET 2300, the spectroscopy was performed by Vinko et al.(2010), and the object was identified as a luminous blue variable (LBV) from the narrow H-alpha emission line and no broadened absorption features. we will continue the observations of this object.