The stellar initial mass function (IMF) is the mass distribution of stars with the same origin. This is an essential parameter to understand the star formation process as well as the overall properties of remote galaxies. Since Salpeter first introduced the concept of mass function , a number of observational results support the idea that the IMf has a universal form. On the other hand, the deep imaging observations of several young massive clusters in the inner Galaxy revealed that they have shallow (top-heavy) IMFs, suggesting that the IMF may depend on the environment in which stars form. On this topic, I will briefly present the results of the Open Cluster Survey and show the status of the Gemini GMOS survey of young clusters in nearby galaxies.