Step 1: Meaning of Adipurana.
The word Adipurana means the "first Purana." It is regarded as the earliest among the 18 Mahapuranas.
Step 2: About Brahmapurana.
Brahmapurana is considered the Adipurana because it is placed at the beginning of the list of the Mahapuranas.
It deals with cosmology, creation, genealogy, and stories connected with Lord Vishnu and Lord Shiva.
Step 3: Exclusion of other Puranas.
- Shivapuranam: Dedicated to Lord Shiva, not referred to as Adipurana.
- Agnipurana: Focuses on a wide range of subjects but not identified as Adipurana.
- Vishnupuranam: Important Purana but not called Adipurana.
Step 4: Conclusion.
Therefore, the Purana famous as Adipurana is Brahmapurana.