Source? And if it is GlobalFirepower.com as I suspect it is then you should be aware that their figures are generally regarded as inaccurate and as far as Reserves are concerned they include factors such as Irregular Citizen Reserves (where conscription exists it uses the figure of Manpower reaching Active Service age 18-49 annually) and Militarized Civilian Police Forces. I refered to Regular Reserves, which are Operational Reserves and not to be confused with Irregular Civilian Reserves.
Spain in particular has a large civilian Militarized Police Force and it actual military reserve is in fact very small, another problem with the GFP information is that is woefully out of date in many cases, for example in 1990 Italy could field active reserves of over 240k and yet in 2010 that figure is more like 38k. This true of other nations such as Germany and particularly Spain, this is largely because both Spain and Germany has ended conscription (Germany recently, Spain in 2001) and the figures do not accurately represent the reality today. (Spain, according to the IISS has reserves of approx 76k as of 2010), Spain in 1989 could field over a million trained reserves..today that figure is around 200k if you include the Civil Guard and volunteer Force. Spain's total military personnel is expected to fall to 80k by 2013 as military budgets are slashed.
Germany and its Bundeswehr has reserves far below what you quoted, and are comparable with the UK, although their actual military is smaller overall.
Finland has the largest Regular Reserve in Europe with around 250k reservists (conscription)
Also If you read Military Balance, an annual publication by the International Institute of Strategic Studies, Germany for example had a total active reserve of 144k as of 2010, not the 355k you referenced above and you will have a far more up to date and accurate picture of the strength of the respective Global Militaries.
Also it should be pointed out that military strength doesn't lie in numbers, but effectiveness.