To save an installation space and to improve the utilization efficiency of a recording paper by providing two one-pen-type self-balancing recorder in the same case so that they are symmetrical in reference to the center point of a recording paper.

A self-balancing recorder using a round recording paper has two one-pen-type self-balancing recorder in one case except a sensor. Recording pens 5A and 5B are arranged so that they are symmetrical each other for the center O of a shared round recording paper 4 and record the same physical quantity according to, for example, a symmetrical object and a location. In the recording paper 4 with 1 rotation/7 days, a recording period is changed, for example, to 1 rotation/day. When a perforation is provided at a portion for dividing the recording paper 4 into two portions and at a portion that is away from a center by a specific radius, the recording paper 4 can be used while it is divided into each half and also the half can be separated while it is mounted to a recorder.