This study examined which factors influenced police officers' feeling of ease or difficulty while interviewing suspects. We conducted a self-administered questionnaire survey with police officers (N=183) who had experience in interviewing five or more suspects during the last decade. The questionnaire consisted of three components: (1) characteristics of police officers (five items, including gender, age, police officer rank, number of years that the police officers had engaged in criminal investigations, and the number of suspects the police officers had interviewed to date), (2) characteristics of suspects (52 items, including “foreign national”, “opposite sex”, “juvenile”, “rapid speaking”, and “compulsive liar”), and (3) circumstances of suspect interview (12 items, including “vicious crimes”, “sex crimes”, and “crime with an accomplice”). A total of 64 items for (2) characteristics of suspects and (3) circumstance of suspect interview were rated, using a seven-point Likert scale, by the police officers according to the degree of ease or difficulty while interviewing suspects. As a result, the police officers evaluated that 36 items (the suspect was a “foreign national”, a “compulsive liar”, and “finding faults”, etc.) made suspect interviews difficult, and 10 items (“full confession” and “existence of physical evidence”, etc.) made the interviews easy. If the suspect was accustomed to police interviews, the police officers' evaluations split into difficult and easy. Exploratory factor analysis extracted three factors from 19 items that were selected on the basis of factor loadings 0.40 and over: (1) the suspect's “self protection”, (2) the interviewer's “anxiety reduction”, and (3) “similar demographics” between interviewers and suspects. The “self protection” factor was found to have a significant positive correlation with number of years the police officers had engaged in criminal investigations. By contrast, each “anxiety reduction” and “similar demographics” factor demonstrated a significant negative correlation with them.