1. An external condition control device based on measurement of brain functions to control external device to match the changes of blood amount at a number of sites on brain of a subject acquired by near infrared spectroscopy by using a multi-channel fiber holder installed on outer side of a head of the subject, wherein said control device comprises: a first means for judging and extracting result by independently operating information for each biological functions such as regional site of brain, pulse wave, left-right difference of the brain, and time difference to match blood amount information obtained as time-series information at a number of sites on the brain from said fiber holder; and a second means for preparing a representative value of the values outputted from each of said modules by summing up the weighted values corresponding to introspective theme designated on a controlled device and for controlling external devices by using the value obtained by repeatedly performing the filtering processing of said representative value.