Puppet Book is a new concept of a digital storybook that is incorporated with puppetry. It enables parents to manipulate characters in real-time through a back-of-device interface while reading a storybook to their children. Puppet Book aims to provide enhanced expressiveness for parents and immersion for children. The Puppet Book interface was implemented carefully to minimize parents' task workload and maximize the expressiveness of puppeteering. A user study with 11 parent-child groups was conducted. Parents who easily adapted to the interface showed a higher motivation to tell the story, by identifying themselves with the characters. Children showed increased concentration and motivation for reading.