Provided is a polyorganosilsesquioxane capable of forming, when cured, a cured product that offers high surface hardness and good heat resistance, is highly flexible, and has excellent processability. The present invention relates to a polyorganosilsesquioxane including a constitutional unit represented by Formula (1). The polyorganosilsesquioxane includes a constitutional unit represented by Formula (I) and a constitutional unit represented by Formula (II) in a mole ratio of the constitutional unit represented by Formula (I) to the constitutional unit represented by Formula (II) of 5 or more. The polyorganosilsesquioxane has a total proportion of the constitutional unit represented by Formula (1) and a constitutional unit represented by Formula (4) of 55% to 100% by mole based on the total amount (100% by mole) of all siloxane constitutional units. The polyorganosilsesquioxane has a number-average molecular weight of 1000 to 3000 and a molecular-weight dispersity (weight-average molecular weight to number-average molecular weight ratio) of 1.0 to 3.0. [R1SiO3/2]  (1) [Chem. 2] [RaSiO3/2]  (I) [Chem. 3] [RbSiO(ORc)]  (II) [Chem. 4] [R1SiO(ORc)]  (4)