To obtain low reflectance for a wide wavelength range in the visible ray region compared to the characteristics of a substrate using a chromium base metal film and to flatten the spectral reflectance curve of the substrate in a wide range by forming a thin film having specified optical characteristics to obtain a low reflection thin film substrate.

This substrate has ≤0.1% min. reflectance and ≤2.0% max. reflectance and ≤0.3% average reflectance in the visible ray region and is produced by forming a thin film on a transparent glass substrate by sputtering. Namely, a transparent glass substrate is mounted to face a batch type reactive sputtering target, the device is evacuated, then argon gas and oxygen gas are introduced into the device for sputtering to form a first layer 1 of about 51nm thickness on the transparent glass substrate 4. Then argon gas and nitrogen gas are introduced for sputtering to form a second layer 2 on the first layer 1. Further, argon gas is introduced to form a third layer 3 on the second layer 2 to obtain a low reflection thin film substrate 5 having a three-layer structure.