1. A living body inspection apparatus comprising: a microcomputer configured to obtain a heartbeat interval from a signal which indicates a heartbeat variation; obtain low frequency components (LF), which are within a predetermined frequency range, by conducting a frequency analysis of the heartbeat interval; obtain high frequency components (HF), which are within a predetermined frequency range, by conducting a frequency analysis of the heartbeat interval; define as an index a ratio of the low frequency and the high frequency components, the ratio being represented by LF/HF, wherein the index indicates a variation state of the heartbeat interval; compare the index, which indicates the variation state of the heartbeat interval, with a predetermined reference value; and determine an occurrence of restless leg syndrome, which is represented by RLS, and if said occurrence of RLS is accompanied by an occurrence of a periodic limb movement, an arousal event, a sleep disorder or a combination of at least two of the periodic limb movement, the arousal event or the sleep disorder based on a result of comparing the index with a predetermined reference value.