A lubrication-condition detector detects a lubricant shortage of a target portion that repeats a predetermined operation at a predetermined cycle. The lubrication-condition detector includes: a physical-quantity measuring unit for continuously measuring a physical quantity related to the target portion; and a computer for determining a presence of a lubricant shortage based on the physical quantity. The computer includes: a cycle extractor for extracting a cycle datum per an operational cycle from continuous data including the physical quantity and its measuring time; a representative-value calculator for calculating a representative value for each of plural cycle data; and determining unit for determining a presence of a lubricant shortage based on the plural representative values.