A magnetooptic element whose size is essentially that of a lattice, namely several angstroms in size of magnetic material and which at the same time has its exhibiting magnetooptic effect detectable is provided along with a magnetooptic disk, a memory device and a magnetooptical picture or image display with a storage capacity of several terabits per square inch or more, each using such a magnetooptic element. The magnetooptic element utilizes a gigantic effective magnetic filed based on a spin chirality formed by geometrically configuring the spin orientation and crystallographic structure of a certain solid material. The solid material exhibiting the spin chirality may be such as a pyrochlore type oxide compound whose chemical composition is represented by chemical formula: A₂B₂O₇ where A is a rare-earth element and B is a transition metal, or a pyrochlore type oxide compound whose chemical composition is represented by chemical formula: (A_1-xC_x)₂B₂O₇ where A is a rare-earth element, C is an alkali-earth metallic element and B is a transition metal and where 0x1.