To restrain the pressure loss of a fluid while reducing a cost of a thermal storage device and to further increase heat exchange efficiency between a heat storage material and the fluid.

This thermal storage device 10 is provided with a heat storage module 11 having heat storage material filling spaces 30 for filling the heat storage materials and fluid passages 40 adjoining the heat storage material filling space for passing the fluids. The heat storage module comprises a plurality of stacked flat plates 20. Each of the plurality of plates has the groove-like fluid passages formed on one-side surface thereof and the groove-like heat storage material filling spaces formed on the other-side surface thereof. Surfaces having the fluid passages of a pair of the plates adjacent to each other are stacked on each other so as to face to each other. When the plates are viewed from the surface direction, the fluid passage on the other-side plate nearly perpendicularly intersects with the fluid passage on the one-side plate. The fluid passages perpendicularly intersecting with each other communicate with each other at a position where they perpendicularly intersect with each other.

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