Do you need to get visa for every country you want to travel to Europe with Thai passport?

It depends which countries you wish to visit. Many European Union countries are part of the Schengen agreement which has removed border controls between countries and created a single Schengen Visa which allows travel between these countries. All you need to do is apply for a visa from the first country you intend to visit and that visa is valid in all other Schengen countries. The Schengen countries are: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain and Sweden, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta,Commonwealth Poland, Slovakia, Slovenia and Switzerland. Note that neither the United Kingdom (Britain) nor Ireland are part of the Schengen Agreement so if you want to visit either country you will need a visa for the UK or Ireland.