The endoplasmic reticulum (ER) plays indispensable roles as a source and sink of Ca²⁺ in both neuronal and glial cells in the central nervous system (CNS). Although intraluminal Ca²⁺ dynamics within the ER is crucial for neuronal/glial physiology and pathophysiology, technical difficulties have impeded direct analysis. In this study, we developed and used a genetically encoded ER Ca²⁺ indicator, G-CEPIA1er to visualize Ca²⁺ dynamics within the ER in neurons and astrocytes. We found ER Ca²⁺ replenishment by intraluminal Ca²⁺ diffusion throughout the ER of dendrites and spines, indicating that the ER functions as a pipeline to redistribute stored Ca²⁺ in neurons. Furthermore, G-CEPIA1er enabled highly sensitive and selective detection of ER Ca²⁺ release as a decrease in ER Ca²⁺ concentration. This allowed us to reveal a novel mechanism of Ca²⁺ release from the ER in astrocytes. Collectively, these ER Ca²⁺ visualization studies provide important new insights to Ca²⁺ handling in neurons and astrocytes, which should be the basis of CNS pharmacology in regard to Ca²⁺ signaling.