How can I find out list of all device drivers installed in my ubuntu. I need list of device drivers not kernel drivers.
Linux (and Ubuntu as well) doesn't have separate entity as "device drivers", Linux has kernel modules which could be called "drivers" for real or virtual hardware depending on their functionality.
cat /proc/modules to see list of loaded kernel modules. Also you can see list of all available (installed) kernel modules in system using:
ls -R /lib/modules/`uname -r`/kernel/