【Background】The rescue workers have felt many stressor of rescue work at disaster. The stressor that rescue workers felt was called “CIS （Critical Incident stress）”．It is necessary to find mental health of rescue workers. No scales to measure up CIS of rescue workers was found. Therefore, we studied analysis of the concept of CIS to develop scales for stressor of rescue workers. The concept analysis was conducted to describe the concept and use of CIS, and thought advantage in expressing an operational definition in disaster study. This analysis is important to examine the concept of CIS for structure and function to promote an understanding of the mental health of rescue workers.【Method】This concept analysis was conducted using approach developed by Walker and Avant approach. This analysis declares difference of definition between stressor and CIS academically and technically used in a society, and define clearly meaning of CIS. The concept analysis was conducted in the following databases: PUBMED, CINAHL, MEDLINE, Japan Medical Abstracts society（ JAMAS）, and Kojien and Dictionary of stress as the Japanese dictionary.【Results】Before sensing CIS，rescue workers have individually“ previous experience”，“personality characteristics”， and “family problem”. When rescue workers operated at disaster, they sensed the CIS that related “environment of disaster”， “exposure of human remain regarding rescue work ”，“danger myself”，and “no organization to carry out effective rescue works”．As a result，it was possible that rescue workers would suffer “psychological disorder” and happen “affected rescue worker's lives”．However“ social support” might protect rescue workers from suffering psychological disorder.