The amount of lubricant oil supplied to a bearing is optimized. A main-shaft lubrication device includes a supply device for variably supplying lubricant oil to bearings which support a main shaft, a collection device for collecting, from the bearings, the lubricant oil supplied from the supply device, a measurement device for measuring the amount of lubricant oil collected by the collection device, and a control device for controlling the amount of lubricant oil to be supplied from the supply device.