Unlike his predecessors, who used bulletproof popemobiles or limousines, Francis uses ordinary cars on international trips, often in contrast to the leaders who greet him.
"Maybe I'm reckless but I must say I don't have any fear for myself but I'm always worried about the safety of those who travel with me and above all that of the people that I meet in various countries.
"There is always the risk of a rash gesture by a madman. But the Lord is always there."
The book, called "Travelling," is about the 17 trips to more than 25 countries outside Italy that Francis has made since his election in 2013.
He is expected to make as least two international trips this year, one to Portugal, and another to India and Bangladesh.
He said: "I can't bring myself to move around in bulletproof cars or in closed popemobiles with bulletproof glass."
He said: "I fully understand the needs of security and am grateful (to security forces) but a bishop is a pastor, a father, and there cannot be too many barriers between him and the people."
"Because of this, I said from the start that I would travel only if I could have contact with people."
For the past two years, Italian police have notably increased security in the area around the Vatican, a sovereign state in the middle of Rome, following attacks by Islamist extremists in Europe.
But Francis still uses an ordinary blue Ford Focus when he visits parishes in Rome and insists on light, low-key security.