Where and how did stars form in galaxies? This question must be answered for a full understanding of the star formation process in galaxies. Since stars form in molecular clouds, CO observations that trace molecular gas are necessary. However, CO imaging observations covering an entire galaxy have not been performed extensively, and our knowledge of the spatially resolved physical conditions of molecular gas has been limited. The situation strongly motivated us to conduct multi-CO line mapping observations for more than 200 galaxies. We observed nearby galaxies with the Nobeyama 45-m radio telescope in ¹²CO J=1-0 in On-The-Fly mode. The final observed sample consists of 147 galaxies because of the long delay in setting up the instrument.