We have been developing a method to evaluate the mental health condition of a person by the sound of his or her voice. Now, we have applied this technology as a system to create a smartphone app. Since using voice to measure one's mental health condition is a non-invasive method and as it could be used continually through the smartphone, one carries, unlike a routine checkup, it could be used for monitoring on a daily basis. The purpose of this study is to compare this vitality score and the widely used BDI (Beck Depression Inventory) and evaluate its validity. This experiment was conducted at COI (Center of Innovation) Program of the University of Tokyo with a total of 50 employees of multiple corporations as subjects between early December 2015 and early February 2016. The test subjects were each lent a smartphone with our app recording their voices automatically during calls, and in addition to it, we had them read and record a fixed phrase daily. BDI test was conducted at the beginning of the experiment period. The vitality score was calculated based on the voice data collected during the first two weeks of the experiment and considered it the vitality score of the time BDI was conducted. When these two indicators were compared, we found there was a negative correlation between BDI and the vitality score. Additionally, it was a useful method to identify a test subject with a high BDI score.