A first lens unit performing communication with an image pickup apparatus (10) with a first voltage (V1) and a second lens unit performing communication with the image pickup apparatus with a second voltage (V2) are selectively attached to the image pickup apparatus. The image pickup apparatus includes a controller (18) configured to operate with a third voltage (V3) different from at least one of the first and second voltages to output a signal for the communication with the first and second lens units, and a determiner (90, 20) configured to determine the type of the lens unit attached to the image pickup apparatus. The controller is configured to produce, as a voltage of the signal for the communication, from the third voltage, one of the first and second voltages corresponding to a determination result of the determiner.