Cutting unit position detection method and cutting device

The invention provides a position detection method of a cutting unit and a cutting device. The cutting device includes: a cutting unit; a blade tip position detection means for detecting the height position of the lower end of the blade tip of the cutting tool; and a control means having a relationship registration unit for registering changes over time in the amount of light received by the lightreceiving unit and emitted from the light emitting unit, the detection method comprising: a relationship registration step for observing the amount of light received over time in accordance with thethermal expansion of the cutting tool; registering, in a relationship registration unit, the relationship between the time from the start of observation and the change in the amount of received light;and a height position detection step of obtaining a reference height position of the cutting unit when the height of the lower end of the blade tip of the cutting tool after the workpiece is processed reaches a predetermined h