An electromagnetic holder is used for vacuum conveyance in automated equipment or industrial robots. A rectifier is a part that turns current ON or OFF based on electric control and converts alternating current into direct current. Electric signals are used to perform ON and OFF control. A rectifier is required when using an electromagnetic holder. A rectifier is an AC-DC converter. This part converts alternating current, whose voltage and current change over time, into direct current, whose voltage and current are constant. Two types of rectifiers are available; a type that performs half-wave rectification of either the positive or negative part of the cycle, and a type that performs full-wave rectification of both parts of the cycle.