  The ALPACA experiment is a project aiming to observe sub-PeV gamma rays for
the first time in the southern hemisphere. The main goal of ALPACA is to
identify PeVatrons, the accelerators of Galactic PeV cosmic rays, by observing
sub-PeV pion-decay gamma rays generated in interactions between PeV cosmic rays
and the interstellar medium. This new air shower experiment is located at an
altitude of 4,740 m above sea level in the middle of Mt. Chakartaya in Bolivia.
The air shower array consists of 401 scintillation counters covering an 83,000
m$^2$ surface area. In addition, a water-Cherenkov-type muon detector array
with an area of 3,700 m$^2$ is installed to discriminate gamma rays from
background cosmic rays. The prototype array ALPAQUITA will start data taking in
2022 and will extend to ALPACA in 2024. We report on a general introduction to
ALPACA, the progress of the project, and the sensitivity to sub-PeV gamma rays.
