1.How to select the type of hearing aid for baby :When baby's language is acquired, it's so important to think about factor for hearing aid type selection. The factor is sound pressure balance between own voice and another voice. Usually box type hearing aid is to which own voice is input more strongly is recommended as hearing aid for baby. From the viewpoint of the own and others' voice sound pressure difference and effectiveness of babies get free from the codes of baby-type hearing aid and noise by touching with clothes, and also BTE type is really ear level aid, the BTE hearind aid is strongly suggested. It has been understood that the peak to change the type of the hearing aid for baby is less than 24 months of 18 months or more, it's shift occured the stability of growth of walking posture and the pinna. The type change month from a baby hearing aid to BTE hearing aid is thought that the pinna grows up, the hearing aid comes to get on firmly, and time when the seat title of the baby was steady is appropriate.2.About selection, recommendation and the evaluation of baby's hearing aidIt was clarified that baby's life environment was the noisy that the effect of the directional microphone and the noise reduction system was able to be expected under. In addition, I evaluate the noise reduction and directional microphone effect by each function was evaluated under some babies' life environments. By my result, the noise was admitted to be controlled. On the otherhand, it was understood that the voice of other children in surroundings was controlled on the playground, and was suggested that a further examination be necessary in the usage of the directional microphone.3.SummeryIt is necessary to recommend to the baby BTE hearing aid. However, we must think the shift to BTE hearing aid when there is an obstacle in the installation. A digital hearing aid that was able to use the directional microphone and the noise reduction system was able to control baby's life environment noise, and the effectiveness was able to be confirmed. However, because a life environment sound and surrounding voices are controlled, it is necessary to select the hearing aid that has the function to switch by the scene in use.