A cardiac potential measuring device comprising: a first electrode and a second electrode； a potential difference acquisition circuitry that acquires a potential difference between the first electrode and the second electrode as cardiac potential； an attachment direction detector that detects an attachment direction that is a direction of a virtual line that connects the first electrode and the second electrode attached to the body of the user； and an attachment direction calculator that calculates and outputs a preferred attachment direction in which the potential difference larger than any one of a first potential difference and a second potential difference is generated.
