Working method using autonomous underwater vehicle

A working method using an autonomous underwater vehicle for working on a work object located underwater or at a bottom of water by using the autonomous underwater vehicle while reciprocating the autonomous underwater vehicle between the work object and a return destination, the working method comprising:

• working on the work object with a work device included in the autonomous underwater vehicle while causing the autonomous underwater vehicle to sail along the work object;
• dropping and sinking a transponder to the bottom of water when one of the two following conditions is satisfied:
• (i) a remaining battery amount of the autonomous underwater vehicle falls below a set value;
• and
• (ii) remaining data capacity that can be stored by the autonomous underwater vehicle falls below a set amount, where work performed by the autonomous underwater vehicle includes storing of predetermined data;
• causing the autonomous underwater vehicle to sail toward the return destination;
• and
• resuming work on the work object by causing the autonomous underwater vehicle to sail from the return destination to a vicinity of a work suspended position, at which the work on the work object is suspended, based on information obtained by acoustic positioning using the transponder that is sunk to the bottom of water.