Provided is a toothbrush having a thin head with which good operability can be obtained. This toothbrush is provided with a head portion (110), which is disposed at the tip side and has a bristle setting surface (111) in which a bundle of bristles is set, a neck portion (120), which extends to the rear end side of the head portion, and a handle portion (130), which extends to the rear end side of the neck portion. The thickness of the head portion is 2.0-4.0 mm. The neck portion is formed in such a manner that the minimum value for the width in a direction that is parallel to the bristle setting surface and orthogonal to the longitudinal direction of the handle portion is 3.5-4.5 mm, inclusive, and the width remains constant or increases gradually from the position of said minimum value toward the rear end side. If the width at a position separated by 10 mm from the position of said minimum value in the neck portion toward the rear end side parallel to the bristle setting surface is defined as W mm and the thickness in a direction that is orthogonal to the bristle setting surface is defined as D mm, the value of D/W is 0.7-2.5, inclusive, and the coefficient of bending M (mm4) = W*D3 is 165-625 mm4, inclusive.