According to one embodiment, an information recording/reproducing device includes a recording layer, and a recording circuit configured to record information by generating a phase change in the recording layer while applying a voltage to the recording layer. The recording layer comprises a compound including at least one type of cationic element, and at least one type of anionic element, at least the one type of cationic element is a transition element including a d orbital incompletely filled with electrons, and the average shortest distance between adjacent cationic elements is 0.32 nm or less, and the recording layer is provided with a material selected from (i) AxMyX4 (0≦x≦2.2, 1.8≦y≦3), (ii) AxMyX3 (0≦x≦1.1, 0.9≦y≦3), and (iii) AxMyX4 (0≦x≦1.1, 0.9≦y≦3).