Folding hand saw

A folding hand saw comprising:

• a first housing having a first insertion groove, a first pivotal end and a second pivotal end;
• a transmission unit disposed in said first housing;
• a second housing having a third pivotal end pivotally connected with said second pivotal end of said first housing and connected with said transmission unit, a connecting end, and a second insertion groove;
• and
• a saw blade having a forth pivotal end pivotally connected with said first pivotal end of said first housing and connected with said transmission unit such that said saw blade is pivotable relative to said first housing between a folded position where said saw blade is inserted into said first insertion groove of said first housing and said second insertion groove of said second housing, and said connecting end of said second housing is distant from said first pivotal end of said first housing, and an unfolded position where said saw blade leaves said first insertion groove of said first housing and said second insertion groove of said second housing, and said connecting end of said second housing is joined to said first pivotal end of said first housing.