An evaluator includes a heart rate variability analyzer A having a heart rate measuring instrument, a heartbeat interval measuring instrument, a frequency analyzer, a sympathetic/parasympathetic nervous system index analyzer, and a psychiatric symptom/psychotic disorder onset risk calculator, and a random number generation analyzer having a random number input unit, a random number score calculation unit, and a display unit. Frequency analysis of a heart rate measurement and a heartbeat interval measurement of a subject is performed to determine a high-frequency index, a low-frequency index and a ratio therebetween.