To provide an electrochemical element and its manufacturing method wherein a solid electrolyte composed of an LSGM series composition is used, a high characteristic can be obtained in the initial stage, and the high characteristic can be maintained over a long period of time.

The element is composed of a simultaneously calcinated solid electrolyte 1 consisting of (La, Sr) (Ga, Mg)O3series composition with a fuel side electrode 2 and/or an oxygen side electrode 3, and in the particle size distribution of a crystal particle constituting the solid electrolyte 1, a peak of which the frequency is 2% or more in the range of 0.3-1.5 μm of the particle size, and a peak of which the frequency is 2% or more in the range of 2.5-6 μm exist, and the amount of Ni and Zr in the solid electrolyte 1 is respectively 0.01 atom% or less, and the amount of La of the simultaneously calcined fuel side electrode 2 and/or oxygen side electrode 3 is 0.01 atom% or less.

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