1. INTRODUCTION

2. OBSERVATIONS

3. RESULTS
3.1. Total integrated intensity and velocity dispersion maps of the H13CO+ emission
3.2. Physical properties of the H13CO+ clumps
3.3. Comparison between the physical properties of the C18O clumps and the H13CO+ clumps

4. DISCUSSION
4.1. Evolution of dense gas in cluster-forming regions
4.2. Kinematic structures of the clumps
4.3. Clump-clump collision as a possible triggering of cluster formation

5. CONCLUSION