What brain area is referred to as the 24 hour rhythm generator?

The brain area responsible for the 24-hour circadian rhythm is the hypothalamus, more specifically the suprachiasmatic nucleus located on the anterior part of the hypothalamus. This area is responsible in organizing and programming bodily functions (i.e. cortisol secretion) in 24-hour oscillation called circadian rhythms. 

Both of them have a nucleus, golgi apparatus, cell membrane, smooth and rough endoplasmic reticulum, lysosome, and ribosomes.