Defence minister also ordered the deployment of destroyers equipped with SM-3 ship-to-air missiles to Japanese coastal waters.
Japan has activated missile interceptors and is preparing to shoot down any fragments from a North Korean satellite that may fall on Japanese territory.
Defence Minister Yasukazu Hamada on Saturday instructed troops to ready PAC-3 surface-to-air missiles in southwestern Japan, including Okinawa and nearby islands, in an area believed to be under a flight path of a North Korean rocket that will carry the satellite.
He also ordered the deployment of destroyers equipped with SM-3 ship-to-air missiles to coastal waters, according to a ministry statement.
“We are making the necessary preparations because of the possibility of issuing an order to destroy ballistic missiles and other objects,” it said.
Hamada instructed troops to “implement measures necessary to limit damage in the event of a ballistic missile falling”.
An order to fire missiles has to be approved by the prime minister.
North Korea’s leader Kim Jong Un said earlier this week its first military spy satellite will be launched on an unspecified date.
In 2012 and 2016, North Korea tested ballistic missiles that Pyongyang called satellite launches. Both missiles flew over the Okinawa region.
North Korea has test-fired about 100 missiles since early last year, saying it was responding to joint US-South Korean military manoeuvres it calls an invasion rehearsal. Several of the missiles flew over Japan or landed off the northern Japanese coast.
Last week, North Korea test-launched a solid-fuelled intercontinental ballistic missile for the first time.
North Korea is expected to carry out more weapons tests as the United States and South Korea continue their joint air exercise into next week.
On Tuesday G7 foreign ministers meeting in Japan demanded North Korea refrain from any further ballistic missile tests following a spate of launches this year. The group of rich nations also warned Pyongyang against carrying out an expected nuclear weapons test, and said there would be a “robust” response if it did not comply.