To provide a recorder capable of simply recording a moving average value with fixed reliability without providing a timer in the recorder with a configuration for periodically collecting data.

A recorder 1 includes: a first input processing part 11; a second input processing part 12; a third input processing part 13; and a fourth input processing part 14 which perform processing for fetching a plurality of kinds of input signals from an inflow seawater temperature sensor 110, an outflow seawater temperature sensor 120, a pH sensor 130 and a residual chlorine sensor 140 at a predetermined period to be converted into a plurality of kinds of data; an operation part 20 which calculates operation values at the predetermined period based on a predetermined kind of data; and a recording part 30 which records the plurality of kinds of data and the operation values. The operation part 20 has an operation storage part 22 which stores the predetermined number of operation values calculated at the predetermined period, calculates a moving average value by dividing the total of the predetermined number of operation values stored in the operation storage part 22 by the predetermined number, and the recording part 30 records the moving average value.