Hyper-Kamiokande is a next generation underground water Cherenkov detector, based on the highly successful Super-Kamiokande experiment.
It will serve as a far detector, 295km away, of a long baseline neutrino experiment for the upgraded J-PARC beam.
It will also be a detector capable of observing --- far beyond the sensitivity of the Super-Kamiokande detector --- proton decay, atmospheric neutrinos, and neutrinos from astronomical sources.

The inner segment called the Inner-Detector has a cylindrincal shape of 70.8m in diameter and 54.8m in height.
This main active volume for physics measurments is viewed by an array of 40000~inward-facing 20" photosensors, which provide a photo-cathode coverage of roughly 40%.

Hyper-Kamiokande employs a ring-imaging water Cherenkov detector technique and as a consequence, the capability of a water Cherenkov detector largely relies on the performance of its photosensors.
The dimension of the photo-sensors and their density are subject to an optimization that takes into account the required signal identification efficiencies, background rejection power, and cost.

In this presentation we will discuss the physics potential of Hyper-Kamiokande with emphasis of non-accelerator physics.