Shijuurou Ohara (大原 四十郎 Ōhara Shijūrō) is Nanako's father. He is a famous author of many popular books. He is overprotective of his daughter and worries too much about her. He is often seen to disrupt any important matters at hand whenever he has the most extremely subtle (false) hint that Nanako may be in trouble. He disapproves of Shin-chan's love for his daughter though they both band together in keeping an eye on her.
In the anime, no reference is made to Nanako's mother and Shijūrō's wife, but in the manga she does appear (although her name is unknown).
His first appearance is in episode 236c. In this episode he has a different appearance to his appearance in later episodes of the anime.