Interior Ministry state secretary Bostjan Sefic also said 100-120 customs police would join Slovenian soldiers, regular police and private security firms in dealing with an influx that has strapped the country's limited resources.
The pledge of 400 extra border guards from other European Union states was made at a meeting on Sunday of EU and Balkan leaders that agreed 17 steps to share the burden of the biggest migration crisis to hit Europe since World War Two.
"The first five policemen from Germany are expected to arrive tomorrow," Sefic told a news conference in Ljubljana. The rest of the police officers are to arrive within a week.
Sefic said the 400 would come from Germany, Austria, Italy, Hungary, the Czech Republic, Slovakia, Spain and France. Eight Austrian police officers arrived earlier to assist Slovenia.
Slovenia also plans to hire about 250 unemployed people to help run migrant reception centres.
Slovenia's premier warned shortly before Sunday's deal was struck that the 28-nation EU faced break-up if its members did not stop bickering and agree a plan to tackle the protracted influx of refugees and migrants trekking up through the Balkans from the Middle East, Africa and Asia.
Since Hungary's anti-immigrant government sealed off its border with Croatia 10 days ago, causing the migrant wave to shift westwards to Slovenia, 86,500 have poured into the country, almost all of them bound for preferred destinations in wealthier western parts of the EU, especially Germany.
On Tuesday about 14,500 were in Slovenia, a country of 2 million people, hoping to continue their journey to Austria later in the day or on Wednesday. More were on their way from Croatia, the flow unrelenting despite descending winter cold.
Sefic said Slovenia would consider putting up fences on border crossings with Croatia only if Sunday's accord did not succeed in smoothing migrant flows and "if things go entirely in the wrong direction".