According to one embodiment, an information recording/reproducing device includes a recording layer and a driver section. The recording layer has a first layer including a first compound. The first compound includes a mixed crystal of a first oxide containing a first metallic element and a second oxide. The second oxide has a crystal structure being same as the first oxide and contains a second metallic element different from the first metallic element. The driver section is configured to produce state change in the recording layer to record information by at least one of application of voltage to the recording layer and passage of current to the recording layer. Composition ratio of an element having a smaller ionic radius of the first and second metallic elements is not less than percolation threshold of a lattice formed of ions of the first and second metallic elements based on the crystal structure.