The present technique discloses a buck-boost converter. According to a detailed example of the present invention, a number of switching elements of a buck-boost converter is reduced compared with a conventional buck-boost converter, and thereby a buck mode and a boost mode are performed with reduced overall conduction loss and switching loss. In addition, a buck-boost converter that is capable of stepping up and down an input voltage over a wide range using a single control device, that has a simple structure, that has inexpensive manufacturing costs, and that has a high circuit integration density can be realized by configuring the buck-boost converter to connect a two-phase interleaving boost converter unit to a single-phase buck converter unit.