We developed a one-shot passive Fourier spectrometer to integrate with wearable devices for non-invasive blood glucose measurements. The apparatus was designed with a N.A. of 0.77 for passive spectroscopy of the living body. The field curvature due to the increased N.A. was improved by combining an imaging lens with a phase shifter. Because the apparatus was configured with two lenses, the transmission was high and the optical axis length was 14 mm. In addition, the apparatus was equipped with a multi-slit to prevent loss of interference sharpness. The multi-slit was designed with 5 lines with aperture patterns that enabled the detection of glucose. We measured a blackbody to evaluate the apparatus.