Liquid deterioration determination device and hydraulic unit

A liquid deterioration determination device comprising:

• a liquid level gauge into which a liquid is introduced and that has translucency;
• a casing attached to an outside of the liquid level gauge;
• a light receiver provided integrally within the casing and configured to receive
• detection light transmitted through a liquid introduced from a liquid tank of an external device or
• detection light reflected by the liquid;
• and
• an electronic control device configured to be operatively connected to the external device to determine a degree of deterioration of the liquid when the external device is in a stable operation state,
• the light receiver being configured to output
• a first detection value representing an amount of a light component of a first color included in the detection light transmitted through the liquid or the detection light reflected by the liquid and
• a second detection value representing an amount of a light component of a second color included in the detection light transmitted through the liquid or the detection light reflected by the liquid, the second color being different from the first color,
• the electronic control device being configured to determine the degree of deterioration of the liquid based on a ratio of the second detection value to the first detection value when the external device is in the stable operation state, and
• the stable operation state of the external device being determined by referring to an operation time or a temperature rise of the liquid after starting an operation of the external device.