Scientific investigation or evidence is becoming increasingly important. Especially, there has been a dramatic increase in DNA testing. However, if the scientific evidence is false, this might lead to false accusation. It is difficult for laypersons including judges to understand and evaluate scientific evidence. Therefore, legal regulation is required for scientific examination or evidence. The Japanese Code of Criminal Procedure has the concept of expert evidence/examination that originated from “Gutachten” of German Law. Expertise, which may be scientific or nonscientific, is required because it does not belong to rules of thumb. Expert examiners have the dual character of being judges’ assistants and evidence themselves in the Japanese and European continental legal systems. In the Anglo-American legal system, experts are merely a type of witness（expert witnesses）. They work for the party（prosecutors or defendants）and impartiality is not required of expert witnesses. In contrast, expert examiners are appointed by judges and impartiality is required and expected of them. However, the legal status of expert examiners does not necessarily guarantee the appropriateness of expert evidence/examination. We should consider the system required for maintenance and improvement of quality. Expert examination at the investigation stage is different from that at the trial stage. It is requested by police officers or prosecutors. Judges and defense lawyers have no involvement in the selection of expert examiners and assignment of examination theses and materials. Expert examination requested by investigators might be influenced by unconscious biases. The major part of expert evidence presented in criminal trials is presented at the investigation stage. We must consider the appropriate system for handling expert evidence, with a clear picture of expert examination for investigation in mind.